In Microsoft Exchange Server 2019 or Exchange Server 2016, consider the following scenario:
You send an email message that has an attached email message to User A.
The attached email has more than two recipients in the To line.
User A uses the mobile application that connects to Exchange Server by using Internet Message Access Protocol (IMAP).
User A can't download the email message and the mobile application may crash.
In this situation, when you run the FETCH (BODYSTRUCTURE) command of IMAP, you may find a space is inserted between each recipient. This violates RFC 3501. For example, there's a space between brackets:
(("user1" NIL "user1" "mydomain.local") ("user2" NIL "user2" "mydomain.local"))
To fix this issue, install one of the following updates:
Learn about the terminology that Microsoft uses to describe software updates.