Error occurs while sending mail & e-mail is lost
An error occurred while sending mail : The mail serνer sent an incorrect greeting: concurrent connection limit in Aνast exceeded (pass:0, processes: thunderbird.exe[50]).
A previous update claimed to have addressed this but it's still there...
Krejt Përgjigjet (1)
It's generally recommended to disable any antivirus program option for scanning outgoing mail or secure (SSL) connections.
http://kb.mozillazine.org/Antivirus_software
Do this for Avast and see if the error remains:
https://help.avast.com/en/av_free/17/settings_sh_mail_basic.html