Some emails sending as plain text after migration to Exchange Online

Copper Contributor

I've migrated many customers from IMAP email accounts to Microsoft Exchange Online accounts. It usually works very well. I've had two customers who have had issues with regards to some emails being sent out as plain text instead of HTML. For example if they send a simple email with a link to a website then the receipient gets the following: 





content-Transfer-Encoding: base 64



The Exchange accounts are brand new so none of the defaults could have changed. My thinking is it has something to do with the address book that has been imported into the new M365 Exchange.  Has anyone else experience this or got any idea on how to resolve it?

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