5.3.4 Maximum Body Parts error makes no sense

New Contributor

So I have one user who is plagued with one of the weirdest problems I've ever known in 30+ years of working with exchange - this is on Office365

She is sending emails from Outlook on Windows but then getting an NDR:


Delivery has failed to these recipients or groups:

email address here
Your message is larger than the size limit for messages. Please make it smaller and try sending it again.

Diagnostic information for administrators:

Generating server: GV1PR02MB8281.eurprd02.prod.outlook.com

email address here
Remote Server returned '554-5.3.4 Content conversion limit(s) exceeded 554 5.3.4 STOREDRV.Submit.Exception:ConversionFailedException; Failed to process message due to a permanent exception with message [BeginDiagnosticData]Content conversion: Maximum number of body parts (250) per message exceeded ConversionFailedException: Content conversion: Maximum number of body parts (250) per message exceeded[EndDiagnosticData]'


That's not the weird part, the weird part is as follows:


1) Any other user can send the exact same message with no problem whatsoever

2) If I run an office repair (full online) or uninstall and reinstall office, then the problem goes away and her emails send again - for a short time, after about 20-30 emails they all start failing again with the above error.

3) None of the failing messages show up in exchange logs at all that I can find, ones that succeed I can see, ones that fail for other valid reasons I can see, but these 5.3.4 emails are just not in the logs at all, it seems like the server rejects them even before they enter mail flow logging.


This is a largish and complex email they are trying to send, it does have a lot of inline images and some tables that I would expect to run the email up to around 30-40 parts (not sure how to check it). When this email is generating the 5.3.4 she can still send basic emails, it's only these complex ones that fail - but it's not the email that is the problem, other staff have been sending the same email in bulk (we are a PR company, it's a weekly mailer we send out to journalists) with no issues whatsoever, and as stated if we repair or reinstall office they temporarily send and then suddenly start failing again.

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Does anyone have ANY ideas? I can add to the list of things that fix the issue temporarily but then it re-occurs after a number of emails: A completely different, known good computer, clean user profile - same thing happened, user was able to send the emails fine for a few hours and then every one bounces with the body parts message.