Mailer-Daemon Errors Explained

An error message from AOL's email delivery subsystem (mailer-daemon@aol.com) indicates that there was a problem in delivering your message to its destination. When you receive an error from our mail system, your message will be returned to you along with an outline of the mail delivery problem.

This document will help you become more familiar with the format and content of our mailer-daemon error messages so you can identify delivery problems and possibly correct the situation.

Due to the fact that AOL's mail servers are hosted in the US, contact details shown in the bounce message you receive are for AOL's US offices and therefore differ from the contact details provided in the other pages.


There are five portions of the error report that you should be familiar with:


1. The first thing you will see is a line that tells you the date and time that your email was received by AOL's mail system. It will look something like this:
"The original message was received at Tue, 14 Jul 1998 20:48:05 -0400 (EDT) from your.domain.org [x.x.x.x]"
Your.domain.org will be the domain from which you sent your mail and x.x.x.x will be the IP address from which your mail originated.

2. The next section will be a brief message from the AOL Postmaster. The text there will be updated on an as-needed basis. The current text contains an explanation of how to read the error report. This is the current text:

*** ATTENTION***

Your email is being returned to you because there was a problem with its delivery. The AOL address that was undeliverable is listed in the section labelled:
"----- The following addresses had permanent fatal errors-----."

The reason your mail is being returned to you is listed in the section labelled:
"----- Transcript of Session Follows-----".

The line beginning with "<<<" describes the specific reason your email could not be delivered. The next line contains a second error message that is a general translation for other email servers.

Please direct further questions regarding this message to your email administrator.
--AOL Postmaster

3. The third section has the heading
-----The following addresses had permanent fatal errors----.
Here you will find the AOL address(es) that had mail delivery problems.
----- The following addresses had permanent fatal errors -----
someunknownaddress@aol.com

4. The fourth section is the most important in terms of determining why your email could not be delivered because it contains the specific error assigned to the delivery problem it experienced. This error will also be delayed when attempting to complete a manual mail transaction via a telnet session with our mail relays.

The section heading is
----- Transcript of session follows -----
and its contents will look something like this:
----- Transcript of session follows -----
... while talking to air-xg02.mail.aol.com.:
RCPT To:
<<< 550 MAILBOX NOT FOUND
550 ... User unknown
Reporting-MTA: dns; rly-xg06.mx.aol.com
Arrival-Date: Mon, 15 Dec 2003 19:29:05 -0500 (EST)

Final-Recipient: RFC822; someunknownaddress@aol.com
Action: failed
Status: 5.1.1
Remote-MTA: DNS; air-xg02.mail.aol.com
Diagnostic-Code: SMTP; 550 MAILBOX NOT FOUND
Last-Attempt-Date: Mon, 15 Dec 2003 19:29:07 -0500 (EST)

The line beginning with"<<<" describes the specific reason your email could not be delivered. The next line contains a second error message which is a general translation for other email servers. Each AOL address that could not be delivered will be listed in the Transcript of Session with an error code. For a list of some of the more common error codes, see below.

5. The last section heading is
----- Original message follows -----
and it contains your original email that we are returning to you as "undelivered."
Here are some common errors, with brief explanations of how they pertain to our mail system:

  • Non-Spam Mail Problems
  • RTR Blocks
  • HVU Blocks
  • DNS Blocks
  • RLY Blocks
  • ISP Blocks

Non-Spam Mail Problems:

  • 550 "username" IS NOT ACCEPTING MAIL FROM THIS SENDER

This error indicates that the AOL member has configured this account, possibly inadvertently, to only accept email from certain addresses and/or domains on the Internet. Using Email Controls, the member will have to modify those settings to receive mail from you. AOL Postmaster can not override these member defined settings. We respect members' privacy and their ability to control their own email. Postmaster will not forward the email for you.

  • 550 MAILBOX NOT FOUND

This error indicates that the AOL member no longer exists on AOL or the email address is mis-spelled.

  • 550 SENDER DOMAIN NOT FOUND IN DNS
  • 550 REQUESTED ACTION NOT TAKEN: DNS FAILURE

These errors indicate that there are DNS resolution problems somewhere between your domain and AOL. This usually means that AOL is unable to resolve your domain name in DNS before accepting that mail for delivery. Make sure your email address is properly configured in your mail client. You may need to contact your email administrator for assistance. The network administrator for the site may have to modify their resource records in DNS.

  • 552 MAILBOX FULL

This error indicates that the AOL member's mailbox is full. The member will have to free some space in the mailbox before additional email can be received.

  • 552 MESSAGE EXCEEDS MAXIMUM FIXED SIZE

This indicates that the mail sent was larger than AOL currently allows. The largest piece of email that an AOL member can transmit or receive via the Internet is 16 megabytes. This includes the message text, headers and the attachment combined. These sizes are fixed and cannot be overridden.

    The message text detailed below is sent from servers hosted by AOL Inc. For this reason the contact details shown are for the AOL Postmaster team based in Virginia, US.

  • RTR Blocks:
    554 RTR:BB

The IP address you are using to connect to AOL is a dynamic (residential) IP address. AOL will not accept future email transactions from this IP address until your ISP removes this IP address from its list of dynamic (residential) IP addresses. For additional information, please visit http://postmaster.info.aol.com.

AOL works with many ISPs to maintain lists of dynamic and residential IP addresses. Per our email guidelines, we do not accept mail from these addresses, as it is difficult to determine who is responsible for mail being generated by these IPs. If you feel that your IP address has been listed with us in error, please contact your ISP and have them contact AOL through their normal channels. The Postmaster cannot remove IP addresses from this block unless it is at the request of the ISP's administrator.

  •  554 RTR:SC

The information presently available to AOL indicates that this server has been repeatedly used to transmit unsolicited bulk email to AOL. Based on AOL's email policies at http://postmaster.info.aol.com/guidelines/standards.html, AOL cannot accept further email transactions from this server for an extended period of time. Please have your ISP/ASP contact AOL to resolve the issue at 703.265.4670.

This error message is indicative of a block due to successive dynamic blocks issued against your IP address. We recommend that you fill out the Feedback Form asking for a Feedback Loop so that you can monitor your spam reports. The block may be removed if significant improvement in these levels is observed.

  • 554 RTR:DU

The IP address you are using to connect to AOL is a dynamic (residential) IP address. AOL will not accept future email transactions from this IP address until your ISP removes this IP address from its list of dynamic (residential) IP addresses. For additional information, please visit http://postmaster.info.aol.com.

AOL works with many ISPs to maintain lists of dynamic and residential IP addresses. Per our email guidelines, we do not accept mail from these addresses, as it is difficult to determine who is responsible for mail being generated by these IPs. If you feel that your IP address has been listed with us in error, please contact your ISP and have them contact AOL through their normal channels. The Postmaster cannot remove IP addresses from this block unless it is at the request of the ISP's administrator.

  • 554 RTR:GE

AOL will no longer accept email transactions from this server. Please visit http://postmaster.info.aol.com for information on AOL's email policies and guidelines.

The mail you are sending violates one of our guidelines or best practices. Please visit the Guidelines page for more information on how to bring your mail in line with these recommendations. The block against this IP was recently placed and the error message is likely to change within 24 hours providing additional information.

  •  554 RTR:BL

The information presently available to AOL indicates that this server is being used to transmit unsolicited bulk email to AOL. Based on AOL's email policies at http://postmaster.info.aol.com/guidelines/standards.html, AOL cannot accept further email transactions from this server. Please have your ISP/ASP contact AOL to resolve the issue at 703.265.4670.

This error message means that a block has been placed against your IP address because we have received numerous complaints about mail coming from that IP address. Please have your ISP/ASP or server admin call AOL for assistance.

  • 554 RTR:OP

The IP address you are using to connect to AOL is available for free proxy service. AOL will not accept future email transactions from this IP address until this proxy is secured. For additional information, please visit http://postmaster.info.aol.com.

Your IP address appears to be an open proxy. Please secure your proxy to unauthorised use. Your IP will be automatically unblocked once we confirm that it is no longer compromised. The Postmasters will not unblock the IP address while it is open to proxy. If you continue to receive this error for more than 24 hours after your proxy is closed, please complete the Feedback Form.

  • 554 RTR:OR

The IP address you are using to connect to AOL is open to the free relaying of email. AOL will not accept future email transactions from this IP address until this server is closed to free relaying. For more information, please visit http://postmaster.info.aol.com.

Your IP address appears to be an open relay. Please secure your server from relaying unauthorised mail. Your IP address will be automatically unblocked once the server has been secured; this process may take up to 24 hours. The Postmasters will not unblock the IP address while it is open to third-party relay.

  • HVU Blocks:
    554 HVU:B1

The URL (web link) contained in your email to AOL member has generated a high volume of member complaints. Per our anti-spam, Unsolicited Bulk Email policies, AOL will no longer accept email with the URL contained in your message.

There is at least one URL in your email that is generating substantial complaints from our members. If you own all the domains linked to in your email, please contact us to discuss more effectively managing your complaint levels. If you do not own the domain of the problematic link, please have the owner of that domain contact us.

  • 554 HVU:B2

Per our anti-spam, Unsolicited Bulk Email policies, AOL will not allow traffic from Internet senders that uses the r.aol.com redirector URL.

Your email contains the r.aol.com redirector in conjunction with a URL you are sending. Please remove this URL from your email. The Postmasters will not exempt anyone from this rule as the use of this redirector is restricted.

  • 554 HVU:B3

AOL is unable to parse the URL contained in this message. Per our anti-spam, Unsolicited Bulk Email policies, AOL will not deliver emails with unparseable URLs.

A URL in your email is formatted in such a way that our filtering mechanisms do not recognize it as valid and parseable. Ensure that your mail does not contain any URLs with spaces or hex encoding (http://%20%40%60%80, for example).

  • 554 HVU:SR

The URL contained in your email to AOL members has generated a high volume of complaints. Per our Unsolicited Bulk Email policies, AOL will no longer accept email with the URL contained in your message.

Your email contains some form of redirecting URL which AOL's servers will not accept. Please remove all redirecting URLs from your mail and try your message again.

  • 554 HVU:NR

This email is rejected for containing one or more URLs which do not follow RFC guidelines. For additional information, please visit http://postmaster.info.aol.com or call 888.212.5537.

AOL requires that all URLs contained in email comply with the RFCs pertaining to URL and domain name formatting. Please make sure that all URLs in your email are RFC compliant and try your mail again.

  • 554 HVU:FO

The URL contained in your email to AOL members has generated a high volume of complaints. Per our Unsolicited Bulk Email policies, AOL will no longer accept email with the URL contained in your message.

Some part of the HTML contained in your message is poorly formatted. Please make sure that all HTML in your message is properly formatted to industry standards and try your message again.

  • 554 HVU:FO2

The URL contained in your email to AOL members has generated a high volume of complaints. Per our Unsolicited Bulk Email policies, AOL will no longer accept email with the URL contained in your message.

Some part of the HTML contained in your message is poorly formatted. Please make sure that all HTML in your message is properly formatted to industry standards and try your message again.

  • DNS Blocks:
  • 554 DNS:B1

AOL has determined that you are connecting directly to our mail servers from a residential or dynamic IP. AOL only accepts mail connections from static IPs. For more information, please visit http://postmaster.info.aol.com/info/rdns.html.

Your IP address is denoted by its reverse DNS as being a likely dynamic IP address. If you are on a dynamic IP address, please call your ISP and request a static IP address for your server before attempting to send mail to AOL through that server. If you are on a static IP address, please call your ISP and ask them to establish a reverse DNS record for your IP address, reflecting your correct domain name.

  • 554 DNS:SR

http://postmaster.info.aol.com - The IP address connecting to America Online has a reverse DNS entry that is consistent with residential/dynamic configurations. Residential customers should consult their ISP to ensure their mail application is configured properly. If you are receiving this message in error, please ask your ISP to contact AOL's Postmaster Support at 888-212-5537.

Your IP address is denoted by its reverse DNS as being a likely dynamic IP address. If you are on a dynamic IP address, please call your ISP and request a static IP address for your server before attempting to send mail to AOL through that server. If you are on a static IP address, please call your ISP and ask them to establish a reverse DNS record for your IP address, reflecting your correct domain name.

  • RLY Blocks:
  • 554 RLY:B1

The information presently available to AOL indicates this server is generating high volumes of member complaints from AOL's member base. Based on AOL's Unsolicited Bulk email policy at http://www.aol.com/info/bulkemail.html AOL may not accept further email transactions from this server or domain. For more information, please visit http://postmaster.info.aol.com.

This error message is indicative of a dynamic block on our system. Dynamic blocks are placed on an IP address when complaints go over a certain threshold, and will be removed after complaint rates have been lowered. These are automated blocks and not part of a manually controlled process. Thus these blocks will not be removed manually but are automatically removed within 24 hours. Mail administrators should take this opportunity to ensure that their mail server has not been compromised. If the error message is received beyond the 24 hour period, the mail administrator should complete the Feedback Form to request a feedback loop that will alert them to reported spam from their network.

  • RLY:B2

The information presently available to AOL indicates this server is transmitting unsolicited email to AOL. Based on AOL's Unsolicited Bulk email policy at http://www.aol.com/info/bulkemail.html AOL cannot accept further email transactions from this server. Please have your ISP/ASP or server admin call AOL at 1-888-212-5537, or visit http://postmaster.info.aol.com for more information.

This error message means that a block has been placed against your IP address because we have received numerous spam reports about mail coming from that IP address. Please have your ISP/ASP or server admin contact AOL for assistance.

  • ISP Blocks:
  • 554 ISP:B1

AOL is not currently accepting email from your point or origin through your ISP. Please contact your ISP's Technical Support to resolve this issue. The AOL postmaster team will work directly with your ISP if necessary.

The IP address on your ISP's network has generated a high volume of mail to AOL and has exceeded our rate limit. Possible causes include a compromised or virus-infected personal computer or a non-disclosed server relaying mail within the ISP's network. Please contact your ISP for assistance in securing your computer or have them contact AOL through their normal channels to alert us to the addition of this mail relay.