When a user reads the email coming from another user created by QMM Directory Synchronization, the From field of the message contains the user's name with numbers in the end, for example:
From: John Smith <JohnSmith11675558>
Checking the legacyexchangedn attribute of the user shows that it ends with /cn=JohnSmith11675558
The legacyexchangedn attribute of the target object is generated from the corresponding source object's primary smtp prefix. Some of the characters that can be used in an email address are not valid for legacyexchangedn, for example hash character '#'.
QMM DSA behaves in a similar manner to Microsoft's Recipient Update Service. For example if a user is created with native Microsoft tools having an alias of #serviceaccount, their primary smtp address will be #email@example.com, but the legacyexchangedn will end with user[string of random numbers]. This behavior is by design.