I opened a Premiere Support ticket and basically got nowhere. Kind of understandable, considering the errors are generated from recipient servers, but contacting every external Domain admin is a non-starter:


"Unfortunately, there are no other options to "fix" this issue as we are not in control of the receiving servers and are unable to predict what each of the header sizes will be."


"Removing the outbound connector for Listserv and changing the MX record is an option but it may not resolve the issue because the receiving server only accepts headers smaller than 32KB. Headers cannot be stripped when the message is delivered to Exchange Online Protection, so that would not be plausible as it is not compliant with our standards."


"Simplify the message routing by changing the MX record for listserv.blah.blah to point to the actual list server"


Respectfully,

Matthew Silcox


Senior Systems Administrator

Client Infrastructure Group | Information Services

Kent State University


*    330.672.1290

*    [log in to unmask]<mailto:[log in to unmask]>




________________________________
From: LISTSERV Site Administrators' Forum <[log in to unmask]> on behalf of Eckstine, Nate <[log in to unmask]>
Sent: Thursday, July 21, 2016 12:20:17 PM
To: [log in to unmask]
Subject: Office 365 Headers too large errors in the Daily Monitoring report


Our messaging group looked at this and is going to lessen the header size by adjusting some filtering available in Office 365. What appeared to have happened was Microsoft developed a new enthusiasm for email diagnostics and spam prevention.  The newer products became header heavy without an awareness of the impact on other email systems. My guess at least.



I was looking thru some of the Transport Rule options and I might have found a solution.

It appears I am able to strip out individual header entries

Now the challenge is to figure out which header entries are huge and mostly unnecessary



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