Hi, On Tue, Aug 15, 2023 at 11:53 AM Paul Enlund via Postfix-users < postfix-users@postfix.org> wrote:
> Hi > > One thing to check is that your MX server allowed recipients is in sync > with M365 allowed recipients. > Can you explain more of what you mean here? In this case, the recipient does exist. I don't believe it's ever happened with a non-existent recipient. We aren't pulling the list of valid recipients, but instead just letting their system send us the reject for non-existent recipients. Thanks, Alex > 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, > 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> <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 > > > > _______________________________________________ > Postfix-users mailing list -- postfix-users@postfix.org > To unsubscribe send an email to postfix-users-le...@postfix.org > > _______________________________________________ > Postfix-users mailing list -- postfix-users@postfix.org > To unsubscribe send an email to postfix-users-le...@postfix.org >
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