So it looks like you're trying to send using a from: address which appears to have been removed, disabled or retired. The message is from a server. You need to check if all the addresses offered in Thunderbird as from: addresses are current and valid. But now I see other posts saying pretty much the same, which has me wondering if this is a problem at the server. Who is your mail provider? https://support.mozilla.org/en-US/questions/1014299