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Affordable Email Lists and Domains since 2000
Affordable Email Lists and Domains since 2000
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Affordable Email Lists and Domains since 2000
Affordable Email Lists and Domains since 2000
Affordable Email Lists and Domains since 2000

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guidelines, requirements, and tips for getting list mail delivered
Quick Links to Host Anti-Spam Info on this Page
AT&T (
Juno (NetZero/ Bluelight)
Road Runner (
University of Michigan (
Unfortunately for list owners, the spam situation has reached a point where email hosts are willing to toss out a lot of legitimate email in an effort to reduce the amount of spam delivered to their customers. Customers are demanding better anti-spam protection for their inboxes, and hosts are finding the high costs of processing millions of spam emails per day intolerable.
As a result, most of the large email hosts have instituted anti-spam policies (sometimes referred to as greylisting) that stop deliveries of emails from IP addresses that send a large number of messages to their servers in a specified period of time. The period of time and what is considered a "large number" varies, depending upon the host, and this information is not published. Service providers like WebHelps, that offer email list services using virtual domains on shared IPs, find their mail servers unduly targeted for greylisting. It does not matter that our customers are sending legitimate mail, the large mail ehosts are still flagging it as spam. This is a problem affecting all companies that send a large number of messages to,,,, and similar email addresses - not just WebHelps - and no one has a sure-fire solution.
If you are using a dedicated IP address for your domain/lists, you are able to signup for whitelisting and feedback loop participation at many of the major email hosts, such as Yahoo!, Verizon, Comcast and AOL.
Best Practices Guidelines (to Help Get List Mail Delivered)
While following the guidelines below will not guarantee that all your list mail will be delivered, it will decrease the incidence of it being misidentified as spam:
  1. Immediately remove bad addresses and respond to unsubscribe requests quickly. The No. 1 reason a list gets misidentified as a source of spam, is because there are bad subscriber addresses on the list and the list repeatedly sends to them, even after permanent delivery failure notices have been received. When a receiving mail server sends a permanent delivery failure notice (a "bounce notice"), it expects the list administrator to remove the address so no more emails are sent from the list to that address. Continuing to send posts to known bad addresses is spamming the receiving mail server. You must monitor the list administrator's inbox for bounces and immediately remove any bad addresses from the list of subscribers.
    If, instead of using the unsubscribe instructions provided in your list's trailer/bottom banner, a subscriber asks you to remove his/her address from the list, do so immediately, and report back to the requestor.
  2. Send *only* to the List Address. Avoid sending emails to multiple addresses in the "To", "Cc" or "Bcc" fields.
  3. Draft subject lines with care. Avoid using words, phrases, and symbols that can appear to be spam, such as "free," "limited time offer," or "low-cost," words in all caps, or exclamation marks. Do not use subjects that include words or phrases with a sexual connotation or that includes names of pharmaceuticals, illegal or illicit drugs, or money-making or money-saving schemes. Never send emails with blank subject lines or add "Re:" to your subject as these are both common spam tactics.
  4. Watch your language. If your email contains words or phrases on a host's Banned Phrase List it will not be delivered, and you will not receive a bounce notification.
  5. Be careful when adding links. If your email contains a link with a domain on a host's Domain Black List it will not be delivered, and you will not receive a bounce notification.
  6. Include unsubscribe instructions, instructions for contacting the list administrator, and your mailing address. IMail® allows both an HTML and a plain text header or trailer/footer to be automatically added to all list emails. Typically, these required instructions are put in the trailer. Not only are these instructions required by RFC regulations, but many mail hosts, including AOL and Yahoo!, require them for list mail delivery.
  7. Do not use HTML on discussion list emails. HTML/Rich Text should not be used on emails posted to discussion lists. No good reason exists for using HTML on this type of list, but there are many reasons why HTML should not be used. For indepth information, go to Why and How to Send List Mail in Plain Text. With IMail® it is possible to automatically reject emails containing HTML/Rich Text by creating an inbound rule for the list.
  8. Keep the HTML in your newsletters simple. Do not use any of these types of coding in your emails:
    • Scripts (e.g.. JavaScript, VBScript)
    • Java
    • Frames and IFrames
    • Tooltips
    • Active X
    • Video
    • Audio
    • External Style Sheets
    • Meta Refresh
  9. Reply-to address should be the same as the From address. If sending mail from an email program that will let you set a Reply-to: address for the sending email account that differs from the From: address, make sure you use the same exact address for both. For instance, in Outlook Express and Windows Live Mail, when you create a mail account, on the General tab of Properties are fields for both E-mail Address: and Reply Address:. Leave the Reply Address: field blank and it will default to the E-mail Address: (From:) address.
  10. Do not send attachments, particularly not image files. Rather than sending an attachment via email, upload the file to to your free web space (100MB is included with your WebHelps account), then provide a view/download link in your email. If you want to give list subscribers the ability to upload files to your account's free space, contact your Support Team and request they create a special username/password for subscriber access. FTP Instructions
    The free web space is setup with directory browsing for any folders that do not contain a default page (i.e. index.html, index.htm, default.html, default.htm). Uploading files into a folder in your free web space is a good, no-cost alternative to sending files via email. People can easily be directed to view the directory listing of files you have made available and can view and/or download and save copies to their computer.
    A download link is just like a link to a web page, except it resolves to a file that generally cannot be viewed with a web browser. Simply instruct recipients to right click on the link you provide, select Save target as, and save the file to their computer. Right click on this link: to see how this works first-hand. To further simplify providing files in this manner, most all email programs will automatically convert URLs to clickable links. Therefore, it is not necessary to use Rich Text or HTML in your emails to provide download links. Simply type the complete URL (e.g. in your email and the receiving email program will make it clickable.
  11. Do not send from a free email account. Some hosts automatically reject bulk email sent from free email accounts, like HotMail.
  12. Keep the file size under 1MB (100KB is optimal). If you are sending email in plain text, without attachments, you are probably already doing this. Many mail hosts impose limitations on the size of email that may be received. Charter, for example, limits residential customers to a maximum single message size of 10MB. Rich Text emails will have at least twice as many lines as the same email in Plain Text.
  13. Include your organization's name, physical address, and telephone number. This information should be included in your list's header or trailer so it is automatically added to all emails. Some hosts, including AOL and Yahoo, require this for bulk email delivery.
  14. Send during non-peak hours. Peak hours vary from host to host, so first you need to review your subscriber list to determine where most of the mail is going. Some hosts publish delivery tips that include the non-peak days/times for their mail servers. If you cannot find this information, test sending at different times a day and/or review your bounce notifications to determine if there is a best time of day to send mail to your list.
Email Blacklists
An Email Blacklist is a database of IP addresses and domains used by known spammers. Using this information, anti-spam filters installed on mail servers can reduce the amount of spam they process by blocking email messages coming from those addresses/domains. Blacklists are used by thousands of email hosts as one of their main defenses against spammers. In today's skeptical Internet communication environment, a legitimate email system can also end up being blacklisted, resulting in mail delivery problems and immeasurable costs in lost business. According to a study released in August 2006 by Return Path, Inc.'s, Assurance Services division, seventeen per cent (17%) of permission-based email messages get incorrectly blocked or filtered by the top 12 Internet service providers. Even emails addressed to confirmed recipients may never reach their inboxes.
There are several types of Blacklists, but those most commonly used by anti-spam filters are DNS Blacklists:
  • DNS Blacklists
    Domain Name Server (DNS) blacklists are lists of IP addresses that are sources of unsolicited emails. With the help of these types of lists, mail system administrators can block mail sent from "spamming" IPs and domains. DNS Blacklists are maintained by anti-spam organizations or by individuals. Lists maintained by individuals may not be up-to-date and reliable, particularly those run by anti-spam vigilantes. WebHelps was on a vigilante list for quite some time, for the sole reason that we hosted our servers with Rackspace and this individual listed all of Rackspace's customers, whether or not he had any evidence of spam coming from their servers. Fortunately, very few email hosts use any but the biggest and most reliable blacklists.
  • IP Blacklists
    IP Blacklists block specific IP addresses (and IP ranges), message senders or message recipients (local mailboxes) as determined in the Blacklists. The problem with using an IP Blacklist is that it may cut off legitimate users trying to access sites or blogs, or prevent them from sending email to users.
  • Spam Blacklists
    Spam Blacklists are lists of mail servers or open relays known to be used by spammers to deliver unwanted email. Mail System administrators can use these Lists to block spam transmitted from such sources.
  • Email Blacklists
    Email Blacklists contain known mail servers and email addresses used by spammers. These lists are not frequently used by mail system administrators because of the high probability that legitimate mail is also being blocked.
  • IP blockers & IP Blackholes
    IP Black Hole lists are large repositories of IP addresses that are known to be spamming. These repositories use various reporting mechanisms ranging from human reporting to spam-trap email boxes to determine who is sending spam, and when a spammer is identified by IP or IP block, the spammer is added to the Black Hole list. ISPs and email providers can configure their email servers to query the Black Hole list any time a new email comes in. When a new mail arrives at the server, prior to putting it into the recipient's mailbox, the server will examine the email, and trace its origin. Then it will ask the Black Hole list if this email came from a source that is a currently-known spammer. If the email does not originate from a source known to be spamming, it will be properly delivered into the recipient's email box. If the mail fails the test and is flagged as spam, the email will not be delivered, but rather will be moved to a storage box for future examination by either the mail system administrator or the recipient.
Each Blacklist has its own policies and procedures for how an IP gets on the List, how long an IP must stay on the List, and when/how an IP will/can be removed from the List. There are hundreds of Blacklists, but only a few are widely used. Therefore, even if your email address or IP is on a Blacklist, it may not effect delivery of your mail to most recipients.
To check many DNS Blacklists at once, you can use a service like MXToolbox's DNS Blacklist Check. Links are provided to the site responsible for the List. This can be valuable information if you find you are listed and need information on how to get your address/IP removed. If you are a customer using one of the shared IPs you would check IP or (note: using your own domain is not the same as using your own IP to send list mail.)
Like most email service providers, WebHelps has anti-spam software installed on its mail server which is configured to check the IP of incoming email messages against one or more Blacklists. Currently, WebHelps uses DNS Lists provided by Spamhaus and SpamCop. Mail from senders on either List is automatically deleted, without notice to the sender. WebHelps also maintains a list of email addresses and domains from which it will not accept mail.
Error "554 5.7.9: Message not accepted for policy reasons" when sending email to Yahoo. Why are you seeing this error? Your message wasn't delivered because Yahoo was unable to verify it came from a legitimate email sender. Your email failed one or more of the following industry-wide authentication checks that Yahoo uses to verify emails are truly sent from the domains they claim to originate from:

DKIM (Domain-Keys Identified Mail)
SPF (Sender Policy Framework)
DMARC (Domain-based Message Authentication, Reporting and Conformance)

These standards are designed to eliminate an email user’s exposure to potentially fraudulent and harmful messages and have been adopted by all major email providers and many technology companies.

In April of 2014, Yahoo changed their DMARC policy to proactively protect their users from increasing email spam that uses Yahoo users’ email addresses from other mail servers.This affects only mail with Yahoo addresses on the From: line, like this:

From: “Example Sender”
To: “Favorite Recipient”
Subject: Testing Email

By publishing a “p=reject” record, Yahoo tells other DMARC compliant systems to reject mail from Yahoo users that isn’t genuinely originated from a Yahoo server. Mailing lists are a special case of sending mail on behalf of individuals. The most common solution is to use an address other than your address in the From: line when posting to your list.

Yahoo! Best Practices for Senders. Yahoo! has posted a few best practices for senders here. You will find a list of questions and answers for Postmasters in the Postmaster section of Yahoo! Help Center (see excerpts below).
All IMail List customers running off their own domain and IP Address should be participating in Yahoo!'s Feedback Loop. You will need to utilize the Domain Keys/DKIM feature of Web Administration in order to participate.
Yahoo!'s guidelines include the following:
  1. Ensure that your email address lists are well maintained.
  2. Remove email addresses that bounce. Bounces are an indication that the mail could not be delivered because the user does not exist, no longer exists, or is unable to accept your email. List managers should remove addresses that generate bounces. A particularly popular technique for managing bounces is to use VERP to identify the recipient address that has failed.
  3. Examine your retry policies. Messages that receive permanent errors, such as emails sent to accounts that do not exist or are over quota, should not be retried. Permanent errors that are retried increase the likelihood that delivery will not receive the priority it deserves.
  4. Pay attention to the bounce notices sent by Yahoo!. In particular, Yahoo! will send "500" SMTP response codes to indicate problems you need to investigate. For example, if an email is sent to an invalid recipient, our servers will respond with a "500" range SMTP code, indicating a permanent error.
  5. Don't send unsolicited email. Make sure that all email addresses are confirmed with an opt-in process that ensures the recipient wants to receive your mail. Obtaining permission from a third party to send an email does not ensure the email is solicited. Probably the best way to confirm an email addresses before adding them to a mailing list is by using closed-loop confirmation (sometimes referred to as "full confirmation," "full verification," "confirmed voluntary subscription," or "double opt-in"). In this process, after you receive a subscription request, you send a confirmation email to that address which requires some affirmative action before that email address is permanently added to the mailing list. Since only the true owner of that email address can respond, you will know that the true owner has truly intended to subscribe and that the address is valid.
  6. Provide a method of unsubscribing from your list and your mailing address in each email sent.
The following techniques are said by list owners to be effective in resolving delivery problems:
  1. Send one small, non-list, "good" email to a address from the same address that has been receiving bounces. If it goes through, you will again be able to send list mail to
  2. Change the From: address on your emails, including a different domain, if possible.,, and
Microsoft employs several methods for fighting junk email, including:
  1. Junk Mail Filters (Microsoft SmartScreen®, Symantec Brightmail®, Hotmail Filters)
  2. Phishing Protection
If you are having problems sending the Hotmail, MSN and/or Live, troubleshooting information can be found at the Outlook Postmaster site. If you cannot send e-mail to Hotmail customers, you can create a support request on the MSN Support Home page. Those using a dedicated IP may receive a report on sending problemsby completing and submitting the Sender Information Form.
Senders must comply with the listed guidelines in Microsoft's Policies, Practices, and Guidelines, which include
  1. Microsoft Terms of Use and Anti-Spam Policy;
  2. Technical Guidelines;
  3. Adherence to CAN-SPAM Act;
  4. Authenticating outbound e-mail: Publish Sender Policy Framework (SPF) records; and
  5. Following common e-mailing best practices.
Hotmail/MSN subscribers should be provided with instructions on adding the List Address to their Safe Senders list: From the Hotmail Options screens under Preventing junk email, click Safe and blocked senders. Click Safe Senders. In the text box, type in the List Address, and then click Add to list. These instructions should also be added to the List's "welcome" email to new subscribers.
Microsoft provides several means by which senders can get information about complaints against their IP address and improve delivery rates. Customers using a dedicated IP address should signup for:
The two most important factors that, under normal circumstances, help list messages arrive in Gmail subscribers' inboxes are:
  • The list's From: address (List Address) is listed in the subscriber's Contacts list.
  • Upon receipt of the first List post, a subscriber clicks [Not Spam] to alert Gmail that messages sent from that address are solicited.
When a new subscriber is added, it is a good idea to ask them to do these two things. If you do not want to do this manually, both IMail and LISTSERV lists have automated Welcome messages you can edit to include this information.
Review GMail's Bulk Senders Guidelines for information on best practices to ensure your list mail is delivered to Gmail users. The way Gmail classifies spam depends heavily on reports from their users. Gmail users can mark and unmark any message as spam, at any time. To increase the inbox delivery rate of your messages, make sure all recipients on your lists actually want to receive the mail.
    Important Tips:
  • If using your own domain with your List, publish an SPF Record, and sign with DKIM or DomainKeys when possible.
  • Every subscriber should have opted-in to receive messages from the List. Verification of the subscription email address is highly recommended.
  • Subscribers must be able to automatically unsubscribe from your list through one of the following means:
    • A prominent link in the body of list emails leading users to a page confirming his or her unsubscription (no input from the user, other than confirmation, should be required).
    • By replying or sending an email with an unsubscribe request.
  • To help ensure that your messages aren't flagged as spam, we also recommend that you:
    • Automatically unsubscribe users whose addresses bounce multiple pieces of mail.
    • Periodically send confirmation messages to users. Include each mailing list they are signed up for, and offer the opportunity to unsubscribe from those in which they are no longer interested.
  • All list messages must be formatted according to RFC 2822 SMTP standards and, if using HTML, standards.
  • Messages should indicate that they are bulk mail, using the 'Precedence: bulk' header field.
  • The subject of each message should be relevant to the body's content and not be misleading.
GMail provide their users with a method for sending them feedback about messages flagged as spam -- GMail users have the option of clicking a [Not spam] button for each message flagged by their spam filters. GMail listens to users' reports, and corrects problems in order to provide them with the best user experience. As long as GMail users don't consider list mail as spam, your list shouldn't have delivery problems.
  • My Domain Can't Send to GMail. Use this troubleshooter to diagnose the problem and receive instructions on how to correct it.
  • Receiving an error message? Use GMail's Error Message Search feature to get more information
    AOL Bulk Sender Best Practices. If you are experiencing problems sending to addresses, review the AOL guidelines and best practices for bulk mail senders for important information.
    Many subscribers do not understand how AOL's spam folder works. If/when an email is left in the spam folder when AOL Mail is closed, the email is automatically reported to AOL as being spam. This results in a spam complaint being generated against the sender of the email. You should "educate" your subscribers on how to handle list mail that finds its way into their spam folder. [View sample email to subscribers]
    AOL will reject all emails containing:
    1. a link to a redirected URL. Example: In your email you include a link to our Help section as, rather than the real URL of This can be extremely problematic, as many dynamic web sites (due to necessary programming requirements) have a redirect in place for their homepage.
    2. a link to a banned site. Example: In your email you include a link to a site which AOL has placed on their banned site list. These sites are ones which AOL has deemed to be sources of spam. Unfortunately, AOL does not publish this list, so there is no way to determine if a site is banned by AOL prior to sending out an email.
    AOL Mailer FAQ. AOL posts an important list of questions/answers about sending mail to their site at
    AOL Postmaster Site. The following important anti-spam information can be found at: If you are an IMail® List customer using your domain on a dedicated IP, you should apply to participate in:
    • Feedback Loop. By participating in the Feedback Loop, you will know when List mail is reported to AOL by subscribers as spam. This information is critical to staying off AOL's blacklist by enabling you to find and remove subscribers who no longer want to receive List mail, but have not unsubscribed. In addition, participation in the Feedback Loop is required for whitelisting. [Signup for the Feedback Loop]
    • Whitelisting. AOL's standard whitelist protects mail from some (but not all) of AOL's anti-spam filters. [Apply for Whitelisting]
    What is Comcast doing about spam?. Comcast utilizes a variety of techniques to block spam, including:
    • Reputation Services
      Confirm that the email originates from a reputable source. Determine if sender is a known spammer, and block accordingly.
    • Automated Spam Filtering
      Comcast uses Brightmail to filter outbound and inbound spam using the latest tools and software.
    • Port 25 Blocking
      Port 25 is conduit on a computer that spammers can take control of and use to send their spam - often without the user ever knowing his/her computer has been "hijacked". Comcast works with their customers to block access to Port 25 and protect their PC. Comcast has made it easy for customers to switch to using Port 587, a safer PC configuration, by creating a one-click fix that automatically re-configures computers to use this Port.
    • Spam Blocking (Blacklisting)
      Spammers are constantly looking for new ways to target our customers, often hiding behind legitimate mail hosting and mail forwarding companies without their knowledge. In these situations, Comcast identifies key indicators and patterns of spam and then blocks those senders classified as sending excessive amounts of spam.
    Comcast Blocked Provider Request Form. Comcast provides a Blocked Provider Request Form that may be used to request that an IP address be removed from their blocked sender list. The shared IP addresses for IMail Lists, WebHelps WebMail, and WebHelps POP3/SMTP are and You will find the exact domain/IP that is being blocked on the bounce notification.
    Comcast Feedback Loop Request Form. Those sending list mail via a dedicated IP address should participate in the Comcast Feedback Loop. provides a IP Address Unblock Request that may be used to request an IP address or range be removed from their blocked IPs list. The shared IP address for IMail Lists, WebHelps WebMail, WebHelps POP3/SMTP, and LISTSERV Lists is You will find the exact domain that is being blocked on the bounce notification. recommends rDNS (reverse DNS) contains a name that includes "mail", "SMTP", "relay", or "MX". (For example:,, or WebHelps complies with this recommendation. Reverse DNS for is set to
    Road Runner (
    Sending Mail To Road Runner - General Guidelines.
    Technical and Email Formatting Guidelines. In addition to several technical requirements for mail servers, all of which are fully met by WebHelps, Road Runner specifies numerous requirements for inbound emails and their senders:
    • List administrators must immediately unsubscribe any Road Runner email addresses for which they receive a permanent failure email bounce.
    • Senders must not do anything that tries to hide or forge the sender and sending site of an email.
    • Each mailing must specifically state how each Road Runner customer email address was obtained (i.e. subscription to newsletter, purchase from Acme tools, sign up for Travel discounts, etc.) and must state whether this is a one-time mailing or a recurring mailing. Additionally, such details as the date and time when each email address was obtained, along with supporting documentation such as the Internet headers from email messages requesting signup, or web server logs from addresses collected from signup forms, etc. must be available upon request.
    • All mailings should contain simple and obvious unsubscribe mechanisms. While Road Runner recommends that this be in the form of a working link to a one-click unsubscription system, a valid "reply to:" address may also be used. Requests from Road Runner customers to unsubscribe from mailings must be honored without undue delay.
    • All email must have valid non-electronic contact information for the sender in the text of each email (phone number, physical mailing address, etc.). If this is not readily feasible, there must be a link in each email to such information on the sender's website.
    List subscribers with addresses should be instructed to click [Not Spam] on a message from the List while reading it in their webmail client. This is the best way to keep List messages out of the junk mail folder, and from being misidentified as spam and auto-deleted by the filters.
    Policy & Procedural Guidelines. Road Runner does not filter incoming emails based on content. Emails are refused based solely on the source (i.e., IP address or domain).
    • All email to Road Runner customers must be solicited (i.e., there is an existing and provable relationship between the email recipient and the sender).
    • If a sender generates complaints, bounces 20% or more of the total recipients on its mailings, or bounces are refused by the sender, Road Runner may implement blocks.
    Mail Server Blocks. Senders whose mail server is being blocked will have received an error message that looks like this:
    550 ERROR: Mail Refused - IP_ADDRESS - See
    If you are not sure if your mail server is being blocked, a quick way to check is to use the Road Runner Block Lookup. The shared IP address for the IMail® and LISTSERV List Servers is: WebHelps customers who receive a Mail Server Block error from Road Runner should immediately submit a Help Ticket informing their Support Team.
    Block Lists. If you receive an error message from Road Runner that looks like this:
    ERROR:5.7.1:550 Mail Refused - IP_ADDRESS - See - YYYYMMDD
    you are on a block list from which removal can be requested.
    There are many reasons why your domain or IP might be listed. Check Road Runner Email Error Messages for a list of all its error messages and detailed explanations of what the errors mean. For us to request removal on your behalf, you will need to provide your Support Team with a copy of the error message you received from Road Runner.
    Feedback Loop. IMail® List customers using their own domain on a dedicated IP should apply for participation in Road Runner's Feedback Loop. As a Feedback Loop participant, your IP address will be excluded from blocking by Road Runner's automated tools and you will receive copies of complaints made by Road Runner customers regarding emails sent from your IP address. In exchange, you must promise to take necessary actions to reduce or eliminate all such complaints.
    Your Mail Server or Domain is not Blocked, but Subscribers are not Receiving List Mail. If IMail® or LISTSERV® List subscribers using Road Runner are not receiving list mail, they should
    • review their email security settings to be sure they are not interfering with list mail deliveries;
    • add the list post From: address (List Address) and Sender: address (List Owner Address) to Allowed Senders and Domains. The Sender: address for IMail® lists is listname-owner@listdomain and for LISTSERV® lists is owner-listname@listdomain
  • How does Charter determine email is spam? Charter uses several different tactics to determine if a message is SPAM. The primary tactic is their enterprise anti-spam application.
  • How does Charter handle email that has been flagged as spam? Charter does not accept email that is flagged as spam by their anti-abuse detection system. Email flagged as spam is dropped "on the wire". Anyone attempting to deliver mail to Charter's mail servers that their anti-spam application has flagged as spam should receive an SMTP reply code of "550 Message Rejected".
  • What is an RBL and how is it used? RBL Stands for "Real-time Blacklist". Charter uses multiple RBLs. One RBL is intended to keep track of Charter Customers that are known to have been spammers. These customers have violated the Terms of Service. Another RBL is leveraged to stop inbound mail from spammers whose IPs are known to be owned by spammers. An IP that is on an RBL will not be able to send email to the Charter mail complex
  • Charter Error Codes:
    • 421 Connection Refused - Customer has exceeded the maximum number of messages allowed per hour.
    • 421 Service Not Available - Client IP sending email is on Charter RBL (black list)
    • 421 Lost - Connection was terminated. Possible network connectivity issue.
    • 450 Unable to find: Recipient's domain not found.
    • 452 Too many recipients - The number of email recipients per message exceeded the allowable threshold.
    • 503 Sender Already specified - Too many invalid email addresses
    • 550 Message identified as SPAM -
      The email was flagged as spam by Charter anti-spam detection system. Charter uses several different tactics to determine if a message is spam. The primary tactic is using an industry leading anti-spam filtering application, corroborating feedback from the Internet community and Charter subscribers. A message will not be accepted by Charter mail servers if it is flagged as spam.
    • 550 Relaying mail to - IP attempted to relay, IP not on relay list
    • 552 Message size exceeds allowed maximum message size: 10 Megabytes is the maximum allowable single message size.
    If you receive the error: 550 [MESSAGE ID] Message identified as SPAM - Please visit E5110 The content of the message, or a portion of it, was flagged as SPAM by Charter's anti-spam detection system. If you believe the message was flagged incorrectly, send the original message to (IMPORTANT: The message must not be forwarded. You must resend the original message.)
    Earthlink customers have highly customizable spam settings, spamBlocker, which is probably responsible for your subscribers not receiving list mail. [spamBlocker Information] Have your subscribers review their spamBlocker Settings and make sure they are aware that Senders appear on their Blocked Sender List automatically when they reject Allowed Sender Requests.
    If you are receiving an automated email response with the error message below, your list’s IP address has been prohibited from emailing EarthLink customers. EarthLink blocks IP addresses once they have been associated with spam. If you receive the bounce message below after attempting to send a message to an EarthLink email address, the list's IP address has been blocked:

    #5.5.0 smtp;550 550 Dynamic/zombied/spam IPs
    blocked. Write
    If you have been blocked, there could be several reasons:
    • EarthLink has received numerous spam complaints about your list's mail.
    • Your list's IP address has been listed with one of the reliable RBLs (Real-time Blackhole Lists) which Earthlink uses.
    To have the block removed and be able to send email to EarthLink customers, send an email to with the subject as Blocked 'your list's IP' (example: Blocked The shared IP address for IMail and LISTSERV Lists is: Include the headers and error returned in your original bounced message, if possible. Emails not sent in this format may be rejected. Once the email has been sent, you will receive a ticket number to reference. Your issue will be resolved with 24-48 business hours. Contacting EarthLink outside of this process may result in a delay in resolving your issue. EarthLink Technical Support will not be able to resolve this issue for you. The only way to have your list’s IP address unblocked, is through the above mentioned process.
    Please note that EarthLink’s IP blocks target servers and networks, not email addresses. If and when email blocks are implemented, if someone sends an email message and the sender's IP address or SMTP (outgoing mail) server is on one of these block lists, then the incoming email is blocked. This may unfortunately result in the refusal of some email that is wanted and/or expected. Earthlink cannot make exceptions for individual senders, b or EarthLink accounts in that situationut will accept requests to remove the block. These requests must contain the bounce message received by the sender.
    AT&T (
    AT&T provides a lot of information for both senders and mail administrators on getting mail delivered:
  • Error Messages
  • Unblock Request Form for administrators of mail systems whose messages have been blocked
  • Tips for senders on getting mail delivered
  • Blocked file types
  • AT&T uses the Spamhaus blacklist and Symantec Spam Intelligence to identify and block spammers. Use the Symantec IP Removal form to get removed from the Symantec block list.
    Very important requirements for AT&T deliveries, which are also required by most mail hosts, which are frequently overlooked by list owners/administrators are:
  • Make sure that all legitimate requests for removal from your mailing lists are honored. The easiest way to get your message identified as spam is to send it to people who don't want it or to addresses that are defunct.
    • To do this, check the owner/administrator email account's inbox on a regular basis for bounce notices telling you a subscriber's address is not valid - and IMMEDIATELY remove it from the list of subscribers.
  • Sending bulk electronic messages without identifying, within the message, a reasonable means of opting out from receiving additional messages from the sender (see At&T's Acceptable Use Policy, under Spam/E-mail/Usenet Abuse at
    • To do this, add a trailer/bottom banner to your list that provides subscribers with instructions for unsubscribing via email. It is *not* good enough to give them your email address to contact if they want off the list. They must be provided with a way to automatically and immediately unsubscribe themselves. All our list services provide a way for this to be done via email and/or online form.
  • Sending emails that exceed a recipient's email capacity or that create the potential for disruption of the AT&T network or of the networks with which AT&T interconnects, by virtue of quantity, size or otherwise.
    • To do this, restrict the size of list posts to something reasonable (see above). This is most easily done by prohibiting HTML - require list posts to be in plain text (see Plain Text Sending) - and attachments.
    Verizon's email delivery policy requires:
    (a) All bulk email to Verizon Online subscribers must be solicited, meaning that the sender has an existing relationship with the recipient and that the recipient has not requested not to receive mailings from the sender.
    (b) All subscription-based email must include the sender's valid, non-electronic contact information, including phone number and physical mailing address, in the text of each email.
    The easiest way to comply with (b) is to put the required information in the footer/trailer of list messages.
    List subscribers with addresses should be instructed at signup to submit a Whitelist Request for the List Address. An easy way to do this, is to include the instructions in the "welcome" email automatically sent to new subscribers by IMail® and LISTSERV®.
    U-M ( will block mail from a list that sends mail to invalid addresses. To find out if a particular e-mail address, IP address, or domain is blocked, use the E-Mail Block Status Check Tool. subscribers should add the List Address to their Accept List:
    1. Go to the Server-Side Filters tool ( and log in with your uniqname and UMICH Kerberos password.
    2. On the Existing Rules page, click Accept List.
    3. On the Accept List page, add the List Address, then click Save.
    XMission has two RBLs (real-time black lists): The Botnet RBL and the General RBL. Both are lists of IP addresses which reject messages. You can check if an IP address is on either of these RBLs, and if so, request removal.
    IMail® List customers using their own domain on a dedicated IP address should apply for whitelisting.
    The maximum size of message that will be accepted by XMission is 50mb. Remember that the encoding necessary to send attachments can often be as large as 10mb or 20mb, so be sure you do not send an attachment larger than 30mb with your email.
    Juno / NetZero / Bluelight
    To request information and unblocking of an IP address, use this United Online form. The default IP address for IMail® Lists and the outbound mail server for LISTSERV® Lists is Unless you have an IMail® List that uses a dedicated IP address, that is the IP address you should use for the request.
    To request that your List be whitelisted (a/k/a "Trusted List," "Approved Sender List" - a list on a receiving mail server that prevents future List mail from being blocked) use this United Online form. The IP Address of the Outbound Mailserver for IMail® Lists and LISTSERV® Lists is Unless you have an IMail® List that uses a dedicated IP address, that is the IP address you should use for the request. The Originating Peer Domain for the request is:
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