I've been using Thunderbird for years now and am very happy with it. I know that downloading messages from the mail server there is no prompt for a password no matter which e-mail client you use. I had to change my password yesterday (Saturday) for logging onto My VM or the on line e-mail as I was trying to log on and check something and it wouldn't accept the password. Anyway I managed to change passwords for both and they have the same password now. I then needed to send an e-mail from TB but it's now prompting me for a password. I have entered this correctly and it accepted it but still, every so often prompts me again. I know there is a way of stopping this but can't remember what. Could someone kindly shed some light on this please? Is it something I need to do when logging onto My MV and then going into My Profile that I need to do?
To be honest I'm not aware of any password change issues per se but I'll do my best to help.
Please ensure that the password you changed in MYVM is duplicated correctly in your Thunderbird settings. When prompted for the password don't forget to check the 'remember this password' box.
Accessing webmail will determine if the password itself is correct.
Oh and do you have Thunderbird configured as POP or IMAP?
I'm not sure what else to suggest but there is a possibility that there could be an SMTP authentication issue so please keep us updated.