[1.6.x] Fixed #21566 -- Fixed AttributeError when using bulk_create with ForeignObject.

Backport of bbc73e6a12 from master.
[1.6.x] Added 1.6.3 release note for refs #21566.

Backport of 865392c478 from master
[1.6.x] Fixed #22013 -- Documented difference between SERVER_EMAIL and DEFAULT_FROM_EMAIL.

Backport of 44814e78cc from master