What causes 550 Action not taken ?

[John Levine]

I have a little server that pumps out spam to people who pay me for
it. (Yes, really.)

Looking at the logs, I'm seeing a lot of "550 Action not taken" at end
of data from recipient systems which I believe are running Postfix.
Can someone tell me what that means, so I can tell the recipients to
undo whatever they did to cause it?

The mail typically has a vast spamassasin score and often contains
viruses. Due to the volume it's common to have 20 open SMTP sessions
per recipient. The recipients use it to tune their spam filters, look
for phish campaigns, and the like.

R's,
John

[Viktor Dukhovni]

Post by John Levine
Looking at the logs, I'm seeing a lot of "550 Action not taken" at end
of data from recipient systems which I believe are running Postfix.
Can someone tell me what that means, so I can tell the recipients to
undo whatever they did to cause it?

This is not a Postfix response. Postfix >= 2.3 advertises:

250-ENHANCEDSTATUSCODES

and would generally respond with "550 5.X.Y ...". Not surprisingly,
a search of the Postfix source code finds no such response:

$ git grep "Action not taken"
$

However, this could be the response from a pre-queue virus scanner
(milter or pre-queue filter proxy) or a remote response to a
recipient verification probe. Similar thread:

http://postfix.1071664.n5.nabble.com/550-Action-not-taken-td58892.html