I can send emails without any trouble from my phone or from webmail, but when I try to send a message from Thunderbird—which I've been using without trouble for years—most of the mail doesn't reach its destination. (These are not three different email addresses; they're all the same account.) I don't mean the mail is being caught in the recipients' spam filters. I mean it's just not arriving at all, although Thunderbird treats it as sent mail. I can't even send messages to myself. I checked my outgoing mail settings; they're the same as on my phone, where the mail works fine. I installed a more up-to-date version of Thunderbird to see if that would fix the problem; it didn't. Any troubleshooting advice would be welcome. I'm stumped.