AOL error codes overview

Starting February 1, 2018, Oath (A Verizon company that owns both AOL and Yahoo!) began consolidating sending infrastructures between AOL and Yahoo!. This means that the AOL domains will continue to operate and accept email, but Yahoo! will handle spam filtering and processing.

You can get additional information about the changes and the impact here:

We recommend that you follow best practices for both AOL and Yahoo! during this transition period.

Because the process of consolidating infrastructures will take some time, some AOL domains may be handled by the old AOL infrastructure, while other AOL domains will be handled by the Yahoo! infrastructure. You can get additional information about troubleshooting for Yahoo! here:

You can check if the AOL domains you are sending to are handled by AOL or Yahoo! by entering the AOL domain with MX toolbox and performing an MX lookup. The results will display a Yahoo! hostname if it is being handled by Yahoo!. For example:

  •  hostname =

AOL error codes

One of the best ways to determine what issues may be causing your email to be blocked at AOL is to review their SMTP error codes. AOL provides these error codes with every undeliverable email to help you troubleshoot a possible cause.

The list below outlines some of the more common error codes seen by Return path clients as well as some tips to fix each error. Please visit the AOL postmaster website for a full list of SMTP error codes.

Error Code Format

4.X.X [Code]: 4.X.X error codes are typically temporary in nature. Try sending again in an hour and see if the error code recurs. If you continue to get error messages with this code, lower your hourly volume and increase retry times, ensure you are processing complaints using their complaint feedback loop.

5.X.X [Code]: 5.X.X error codes are usually more permanent in nature and indicate a problem with email from your IP address. Temporarily stop sending to AOL if you see this code and troubleshoot the cause as it may reflect a serious sending reputation issue.

Common error codes

  • 521 Recipient address rejected: This error indicates that the AOL subscriber member email address does not exist. Receiving a large number of bounce messages containing this code may indicate a problem with your list acquisition or bounce process.

HVU (High Volume URL) Blocks

  • 554 HVU:B1 or 554 HVU:B2: AOL found a blocked domain in either the hostname or email headers. This is due to a large number of complaints from AOL members.

Open a support request with AOL (via Yahoo!):

    • Copy and paste the entire body of the sent email, including the URLs of the hyperlinks (not the error message) or the source code of the mail sent to AOL members, which resulted in the error message.
    • In order for AOL to diagnose an HVU:B2 issue and find the URL or domain preventing successful sending, senders must provide AOL with the source of the email that generated the bounce message.

DYN Blocks

  • 421 DYN:T2: This error code indicates that AOL is having a temporary issue with their mail system and they are unable to accept email from your IP. Try sending again at a later time and open a support ticket if you continue to see this error.

CON Blocks

DMARC Blocks

  • 554 DMARC:AOL: This message failed DMARC verification for an AOL domain.
  • 554 DMARC:F1: This message failed DMARC Evaluation due to the policy provided from the From domain. Ensure that all of your IP addresses and domains are up to date in your SPF and DKIM records. You may want to temporarily use a DMARC enforcement policy of p=none until you have identified the cause of the failure.
  • 554 DMARC:TE: This message failed DMARC Evaluation due to an SPF validation error. Check your SPF record to ensure it has the proper syntax and includes all sending IP addresses.

When troubleshooting blocks at AOL, you can open a support ticket (via Yahoo!) directly with AOL to help determine a cause. Prior to opening a support ticket, do your best to troubleshoot and fix the cause and refrain from opening multiple tickets for the same issue or IP address. Duplicate tickets are closed and future tickets from the affected IP address and domain are blacklisted on the ticketing form.

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