DKIM fail only in mail of reading receipt

[loridom]

Versions

• Windows Server Version: Exchange 2016
• Exchange Version: Exchange 2016 CU 23
• Installed DKIM Exchange Version: 3.4.0

Description

Hi,

I have a singular problem.

I've Exchange 2016 CU23.

I have installed DKIM signature on my server and create pertinent DNS record; at this moment I have a key of only 1024bit but I don't think that this is the cause of the problem; both header and body canonicalization are in relaxed mode. All works fine and all mail send from my domain to external of my organization correctly pass dkim verification, except for mail send for reading receipt. If a user (obviously from external organization) flag the function "Request read receipt", when my server send mail of receipt, this mail ever fails check for dkim verification.

I attach screenshot of error in header of mail in this situation.

can you help me for resolve this issue?

Thanks in advance.
Roberto

[a5dev]

If the body of an email is modified, dkim hash will not match. I suspect with read receipt emails the body is being modified somehow. If it were me, I probably wouldn't worry about it. As for the 1024 bit key: Microsoft 365 makes 1024 bit DKIM by default so I also don't think that is causing any issues for you. You might want to consider trying out easydmarc.com. I just started using it and it helped me get a cleared picture of what's happening. It might help you narrow down the problem.