Here is a list of issues that were fixed in this release - build 2.6.28.

Issue Key Description
AVSUPPORT-40875, AVSUPPORT-41794, AVSUPPORT-41895, AVSUPPORT-42375, AVSUPPORT-42529 Some Gmail emails were not delivered to the mailboxes, although they should have.
The issue happened for emails where the first recipient in the envelope recipients list was not a valid recipient (i.e. user does not exist).