I have a single user in my organization of ~650 that is having this strange issue. Occasionally, when she sends emails to a specific user, she'll get a NDR stating
Remote Server returned '550 5.1.3 STOREDRV.Submit; invalid recipient address'
The email headers show strange formatting on the recipient. I'll change the first/last names and domain name for privacy, but leave formatting the same:
From: Jane Doe <Jane.Doe@company.ca>
To: John Doe <JohnDoe<John.Doe@company.ca>>
You notice the recipient is "duplicated" in the angle brackets which causes an invalid address.
This is the only user reporting this issue. She's received 9 NDRs out of 32 emails sent to this recipient. One was a reply, the others were new emails.
We've tried removing the autocomplete entry in Outlook, rebuilding her mail profile, and giving her a new computer to work off of, the issue persists. She does have a fairly large OST file (~20GB), not sure if that is a factor.
We've had her try out webmail, without issue (so far, the ~25% failure rate might not have revealed itself yet in webmail).
We are running off an Exchange 2010/Office 365 hybrid environment. The mailboxes are all hosted in O365. The Outlook client we are using is Office 365 ProPlus. Please let me know if there is any more information I can provide.