https://support.mozilla.org/kb/cannot-send-messages

i really don't know why I am being sent a reply that merely lists all of the stock "fixes" to this problem.

my final sentence above already stated that I have tried all fixes including password resets.

i've now spent five hours trying and retrying "known fixes"

trying to send emails from virginmedia acct(s) using Thunderbird results:

• connected to smtp.virginmedia.com
• Login to server smtp.virginmedia.com failed.

Retry____Enter New Password ___Cancel

• enter your new password
• Login to server smtp.virginmedia.com failed.

as i said, this doesn't appear fixable. so I think i'll find another email client app

i really don't know why I am being sent a reply that merely lists all of the stock "fixes" to this problem.

Not sure what exactly you expected. The only specific information you provided was about deleting your password.

my final sentence above already stated that I have tried all fixes including password resets.

A statement like that isn't exactly useful. It can mean anything, and I'm not going to guess.

i've now spent five hours trying and retrying "known fixes"

Good. Please explain the steps you did and what are the results.

as i said, this doesn't appear fixable.

I suppose that you're not the only one using Thunderbird to access a Virginmedia email account. So chances are it's working just fine for others. The problem is not necessarily at your end, it may well be an issue on the server side of Virginmedia.

so I think i'll find another email client app

That is entirely up to you.

I believe VM uses Yahoo mail infrastructure, and there is a problem sending with such accounts if you have a Reply-to address that is different from the sending address. Do you have a Reply-to for the account?