postfix SASL authentication failed - Internal authentication error

I brought someone in and, after a bit of examination and testing, we added smtp_sasl_mechanism_filter = login to main.cf. That cleared it up.

He explained it forces postfix to do the AUTH LOGIN (that I was doing manually while testing through telnet). smtp_sasl_mechanism_filter doc

I watched with tail -F /var/log/mail.log and the emails were going out. mailq runs showed a shrinking queue and it was good.

Thanks, all!

P.S. Three more notes:

1) I removed smtp_sasl_security_options = noanonymous. This may have been in the right direction, but it didn't get it done.

2) I didn't need to use smtp_generic_maps.

One of the articles had used both of these (and Costin suggested smtp_sasl_security_options as well).

3) This article was helpful in showing how to get Base64 password for manually logging in with telnet with perl -MMIME::Base64 -e 'print encode_base64("john\@example.com\0john\@example.com\0password")';