AOL transmitting 4xx error for user unknown

AOL is currently returning “451 4.3.0 <invaliduser@aol.com>: Temporary lookup failure” in some cases when they really mean “550 user unknown.” This message from AOL should be treated as 5xx failure and the message should not be retried (if at all possible) and the failure should be counted as a hard bounce for list management purposes.
This is something broken at AOL’s end, and the guys with the magic fingers that keep the system running are working to fix it. Right now there doesn’t seem to be an ETA on a fix, though.
Even if you are a sender who is able to stop the retries, you may see some congestion and delays when sending to AOL for the time being. Senders who don’t get the message, or who are unable to stop their MTAs from retrying 4xx mail will continue to attempt delivery of these messages until their servers time out. This may cause congestion for everyone and a noticeable  slowdown on the AOL MTAs.
AOL blog post on the issue
HT: Annalivia

Related Posts

Apparent changes at mail.com

I was poking around at some DNS this weekend and happened to do a MX lookup for mail.com and noticed something changed. Previously mail.com mail was handled by Outblaze (now owned by IBM). It seems, though, that mail.com is now outsourcing their mail delivery to AOL.

Read More

AOL EWL: low complaints no longer enough

This morning AOL announced some changes to their Enhanced White List. Given I’ve not talked very much about the AOL EWL in the past, this is as good a time as any to talk about it.
The AOL Enhanced Whitelist is for those senders that have very good practices. Senders on the EWL not only get their mail delivered to the inbox, but also have links and images enabled by default. Placement on the EWL is done solely on the basis of mail performance and only the best senders get on the list.
The new announcement this morning says that AOL will take more into account than just complaints. Previously, senders with the lowest complaint rates qualified for the EWL. Now, senders must also have a good reputation in addition to the low complaint rates. Good reputation is a measure of user engagement with a particular sender.
This change only reinforces what I and many other delivery experts have been saying: The secret to good delivery is to send mail recipients want. ISPs are making delivery decisions based on those measurements. Send mail that recipients want, and there are few delivery problems.
For a long time good delivery was tied closely to complaint rates, so senders focused on complaints. Spammers focused on complaints too, thus managing to actually get some of their spam delivered. ISPs noticed and started looking at other ways to distinguish wanted mail from spam. One of the better ways to separate spam from wanted mail is to look at user engagement. And the ISPs are measuring engagement and using that measurement as part of their decision making process. Send so much mail users don’t read it, and your reputation goes down followed by your delivery rates.

Read More

Odd Yahoo Bounces

A number of people are reporting seeing a new bounce from Yahoo. “smtp;553 Mail from x.x.x.x not allowed – [10]”. My clients have been asking and other people have been asking about this. It seems that something is changing at Y! More information as I hear it.

Read More