System worked fine until recently. Receive emails no problem, sending emails hit and miss, sometimes one goes okay, then the dread message " an error occurred while sending mail: the mail server sent an incorrect greeting: please try again later." My service provider says my system is trying with the wrong password, the password being used is my user name. I can send messages from my phone no problem which has the same password (obviously). I have checked and the password is correct within thunderbird. I don't understand why sometimes it works and sometimes not. I run windows 10 pro on 64 bit system and keep thunderbird up to date. My service provider is Chess, I was originally with Colloquium and have been migrated through several service providers to reach Chess. Would appreciate any help as can't work out why.