sendmail status and auth advice

[Anton Shterenlikht]

 https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/SMTP-Auth.html
points to
 http://www.sendmail.org/~ca/email/auth.html
which is up to 8.13, last updated in 2006.
The version I have on FreeBSD 11.0-RELEASE-p9 is
sendmail+tls+sasl2-8.15.2_3.
So I'm worried the advice might not be up to date.
Is it?

Trying to find some sendmail docs online I realised
that sendmail.org now points to
 https://www.proofpoint.com/us/sendmail-open-source
which seems to be a for profit company.
And there seem to be no sendmail docs on that site.

Are there still current sendmail docs online somewhere?

I'm struggling to set up sendmail on my server to *send*
only via smtp.office365.com 587 (STARTTLS).
What is the easiest strategy to implement and/or the
easiest guide to follow?

Am I correct that for send only use of AUTH I don't
need to issue or use certificates?

Would be thankful for any advice.

Anton