Invalid characters in UPN and email address

Copper Contributor



Quite a large number of mailboxes are not sync to Cloud because special characters are not supported in Office 365.

Is invalid character support in:

- public folders where email address has special character?

- distribution list?

- mail contact?

Thank you

3 Replies
best response confirmed by NodorinaMing (Copper Contributor)


You'll need to clean that up or prevent the sync of those objects by filtering in AADConnect

here is some info on what is allowed:


and the tool that can help identify and fix these:

I did quite a bit of testing on this, there are some nuances and you can add back addresses with special characters as a secondary alias and that will work. See for more info.


REF to

I have removed invalid characters from all email addresses (not display name). However the mailbox is still not sync to Office 365.


Getting NDR:

Reported error:

550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup

DSN generated by: