I came across an issue where Thunderbird appears to be connecting and using PLAIN TEXT authentication, leaving username and password visible, even though I have Authentication set it to SSL/TLS or STARTTLS.
In order to troubleshoot this issue, I found the following article:
Following the instructions in that article did NOT work!
It says you are supposed to use MOZ_LOG and MOZ_LOG_FILE as of April 2017 however these variables did not work even though it is June 2018. I had to use the old variable names of NSPR_LOG_MODULES and NSPR_LOG_FILE.
The following is the batch file (for Windows 10) that I used and was able to get a log for troubleshooting the authentication and connection to my POP3 and SMTP servers:
set NSPR_LOG_MODULES=negotiateauth:5,POP3:5,SMTP:5,timestamp set NSPR_LOG_FILE=%USERPROFILE%\Desktop\tb-connect.log "%ProgramFiles(x86)%\Mozilla Thunderbird\thunderbird.exe"
Using this log I was able to identify that it was indeed using PLAIN TEXT authentication. I am still in the process of trying to determine if this is a Thunderbird bug or a server side bug and will report back with further details when I have them.
I have posted a Bug Report on Thunderbird site in order to track the issue: