Out of office email stuck in queue as MSMilter give out a 4.7.1 Service unavailable

J-P Methot jp.methot at planethoster.info
Thu May 4 20:46:51 UTC 2023


I'm testing Mailscanner 5.3.3 and Postfix 3.6.2. Postfix and Mailscanner 
are on two different servers. Everything works properly, except if I set 
an autoresponse in roundcube, the email gets stuck in the postfix queue 
with a temporary failure message :

milter-reject: MAIL from localhost[]: 4.7.1 Service unavailable 
- try again later; from=<>

Postfix has three milter setup : opendkim, opendmarc and MSMilter, 
though that last one is written as an IP + port. If I remove MSMilter 
from the list, the email go through without issue. So what I understand 
is that the  Mailscanner milter is not even accepting my email to scan 
it, but instead rejecting it with a temporary failure message, as if the 
server was greylisted. Yet, nothing inside Mailscanner indicates that, 
as the email just sits in queue inside postfix on the origin server.

What could explain this behavior? I've tried setting Treat Invalid 
Watermarks With No Sender as Spam = nothing, but that didn't change 
anything and as far as I'm aware, the email isn't even given a score.

Jean-Philippe Méthot
Senior Openstack system administrator
Administrateur système Openstack sénior
PlanetHoster inc.

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