I can confirm that i am still having the SMTP Authentication error with version 1.5.23 of Mutt when trying to send mail on a Verizon network.
I get around it, like I described earlier by explicitly naming all Authications to use. I compiled my version of Mutt 1.5.23 with the debug option in hopes that i would check various debug logs, after the error occurred. Can someone tell me where these log files are/what their names are? I can't seem to find them readily. Thanks, Russ