External Mail address is being changed while processed from EOP to internal Zimbra Server.

[binodmaharjan_2020]

Co-existence Scenario: Actually I have a Zimbra mail server and office365. All the mail flow is through the Exchange connector.

Till 4th March 2020, I have no issue with mail flow between office365 and Zimbra. I have checked the message trace, it seems fine. 

From 5th March, I have got an error message:

Status: Office 365 received the message that you specified but couldn't deliver it to the recipient (xyz@domain.com) due to the following error:

ERROR: 550.5.1.0: Sender address rejected: domain.com

As per the above error, the address was rejected by the Zimbra Domain server because there was a rule of block own domain if it came from the external organization(For Spoofing).

In-depth I dig the log in Zimbra server, I found strange that is External address i.e. Gmail address=my own domain. so it was rejected.

Mar 5 19:12:15 mail postfix/smtpd[19367]: NOQUEUE: reject: RCPT from mail-pu1apc01lp2050.outbound.protection.outlook.com[104.47.126.50]: 550 5.1.0 <binod.maharjan+SRS=AIPdn=4W=gmail.com=james.bond@mydomain.com>: Sender address rejected: mydomain.com; from=binod.maharjan<+SRS=AIPdn=4W=gmail.com=james.bond@mydomain.com> to=<binod.maharjan@mydomain.com> proto=ESMTP helo=<APC01-PU1-obe.outbound.protection.outlook.com>

how is this happen I am strange, is this issue with Microsoft or else?

[#2]

If you're having trouble receiving mail from outside, you need to find out where the message is failing.

When sending your text message, check the, especially /var/log/zimbra.log, on your MTA server.

It's often helpful to tail the logfile as you send the message:

 tail -f /var/log/zimbra.log

If you see nothing logged (no connection, nothing) then the problem likely either DNS or your firewall.

It will help to migrate Zimbra to Office 365. If there is a line in the /var/log/zimbra.log like:

 postfix/lmtp ... deferred ... connection refused

There is no connection to port 7025 to perform Local Mail Transfer Protocol (LMTP) delivery.

This is nearly always caused by a host that is configured on private IP Space (or using NAT) and that does not have an interface for the public IP address the server resides on. This can be easily fixed by simply using native IP address lookups for lmtp rather than DNS. Alternatively, you could have your internal network's domain name configured to lookup differently internally than it does externally. Using that method is beyond the scope of this document.

[#3]

Hi @Lewis-H,

As per the last logs, I can clearly see there has been a change in the method of sending emails from office 365 to Zimbra. Due to this alteration, Zimbra’s Anti-spam is rejecting email considering it as a Spoof email ( you can see on a log that it is redirecting as a client domain instead of. Hence if you can just make us clarification on if there is any kind of changes on Exchange online routing.

Here I received the email in Zimbra too but just don't know why it is redirecting?