Please also see #16064, the sendmail side of the story.

While building cyrus-sasl, CRAM-MD5 is explicitly disabled.  Is there a
specific reason for this?

I was wondering because I saw the list of SMTP authentication methods
different MUA's support, and DIGEST-MD5 was rare; on the other hand,
CRAM-MD5 seemed to be much widely supported:

http://www.sendmail.org/~ca/email/mel/SASL_ClientRef.html