Yahoo SMTP Deferrals

As I mentioned before … even though I’m participating in Yahoo’s Email Complaint Feedback Loop, I’m still getting deferrals when trying to deliver mail to Yahoo’s mail servers.   I’ve gotten a few complaints, but not nearly enough to really justify having mail delivery deferred.

I think I’ve figured out a bit more about why Yahoo’s mail servers are deferring some of the mail my servers try to deliver to them.

The error being returned by yahoo’s server’s is:

<> Deferred: 421 4.7.0 [TS02] Messages from
temporarily deferred due to user complaints –; see

I think that the phrase ”user complaint’ is not entirely accurate … I suspect that a ‘user complaint’ can also be generated (although not reported as such) by Yahoo’s anti-spam technology.

So I created a new Yahoo email account for myself and subscribed it to one of my mailing lists.   I then waited for mail to start coming in.

What I found was: Some mail was getting categorized as spam and mail was still getting deferred by Yahoo’s servers.

So, what I’m guessing is … mail tagged as spam by Yahoo’s anti-spam system is being categorized as a ‘user complaint’ … which is causing the deferrals (even though there is no specific user complaint).   Unfortunately, the email headers in Yahoo’s mail system do not give an indication as to why a message was considered spam.   There are some headers in the message that might have some information … but it’s all obfuscated.

My system’s mail traffic is still being evaluated by Yahoo … which will take at least two weeks to complete.   Hopefully they will figure out that the mail my system generates is not spam and stop deferring it’s delivery.

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