Hi
One thing to check is that your MX server allowed recipients is in sync
with M365 allowed recipients.
Regards Paul
On 14/08/2023 22:23, Alex via Postfix-users wrote:
Hi,
I have what appears to be a complicated mail loop problem that I can't
figure out. I suspect that their receiving system (M365) is somehow
reinjecting the message back to our mail server after it's been
successfully delivered to them.
We are acting as MX for two small companies, and occasionally, when
companyA emails companyB, it is first received by raven.example.com
<http://raven.example.com>, 209.216.111.115, which is the MX we have
created for them, processed by amavisd, then routed to the destination
through our postfix-out instance xavier.example.com
<http://xavier.example.com>, 209.216.111.114. The companyB server
accepts the message, but then somehow companyA appears to connect to
our server again and send the same message again.
It's very difficult to trace what's happening, so I hoped someone
could help. I think the sending server is somehow reconnecting to our
server and resending the same message, but it eventually dies with the
sending server saying "Error: too many hops". Our server never sees
that message. They have forwarded the bounce to me and I've pasted it
here:
https://pastebin.com/ChcnDwjK
It appears like it delivers five different copies, but each version
has all the received headers of the previous version.
I'm sorry if this is confusing. I've spent probably six hours or more
reading through this one email trying to trace the problem and
correlate it with the postfix/amavis logs. I believe it's only
happened a few times - I don't quite understand all the circumstances
under which it happens. We also don't always see the reject/too many
hops message. Here is a recent one:
Aug 4 09:01:13 xavier postfix-115/smtp[125455]: 88D5F246:
to=<r...@companyb.com>, relay=127.0.0.1[127.0.0.1]:11024, delay=0.67,
delays=0.21/0/0/0.45, dsn=5.4.0, status=bounced (host
127.0.0.1[127.0.0.1] said: 554 5.4.0 id=136757-17 - Rejected by
next-hop MTA on relaying, from MTA(smtp:[127.0.0.1]:11025): 554 5.4.0
Error: too many hops (in reply to end of DATA command))
Any ideas for either what's going on with this email or what I can do
to troubleshoot this further would really be appreciated.
Thanks,
Alex
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