After some testing, more info on this problem. I have a desktop and a laptop, with 2 email accounts with the same provider: the idea being that I can use either account at home or when mobile. it's also proved useful when testing Tbird, as now. The desktop is the PC afflicted by this problem. This morning, I was able to use one of the accounts to send and receive email Ok. After a re-start this afternoon, I can receive but not send email from that account. An exchange of test massages between the PC's established that the mail account on the server was fine - it was the TB software on the desktop apparently malfunctioning when trying to send from the account - the error message was unsuccessful password on login. However, I did get a message box asking for a password, I inserted it and that was sent OK. A comparison of the passwords on both machines showed that somehow ?? the smtp server password for the affected account on the desktop had been deleted. The next attempt at send from the account got that password request, so I ticked the password manager box before inserting the password and then send - fail again. But now the details (account smtp server, username and password) are back in the passwords list. Saved the test message as a draft, restarted TB and tried again to send the draft message - and this time it sent. Really very fluky. I've complained about this before, and it does seem to be machine affected, but it's getting worse. Next time it happens I'll try to get screenshots to post here. the versions of TB on the machines are: desktop (with the problem) - v68.5.0 laptop (no problem) - v68.4.2. I'm not inclined to update the laptop until the desktop issue is resolved. I