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, 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, 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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