Select Signing Domain::
Determines whether to DKIM sign emails using the domain found in the envelope
-from or the from header in the body of the email. The envelope from is also
-known as reverse-path, see {smtp_rfc} section 3.3 and {rfc_5322} section 3.6.2.
+from or the from header of the email. The envelope from is also known as
+reverse-path and RFC5321.MailFrom (see {rfc_5321} section 3.3).
+The from header is also known as RFC5322.From (see {rfc_5322} section 3.6.2).
+
-The envelop from of certain emails, bounces for example, can be empty. In these
+The envelope from of certain emails, bounces for example, can be empty. In these
cases it is desirable to sign them using the domain found in the from header.
+
Additionally, DMARC (see {dmarc_rfc} section 3.1.1) needs the domain found in