Perhaps you could try to adjust your SMTP server port settings. Outlook servers support both ports 587 (STARTTLS) and also port 465 (SSL/TLS). Sometimes one breaks after updates.

• Port 465: A legacy port for SMTPS (SMTP over SSL/TLS). While still used, it's generally recommended to use port 587 with STARTTLS for more-secure email transmission. Try this one and see if that fixes your issue for the time being.

• Port 587: Is the recommended port for secure SMTP communication (SMTP with STARTTLS) when sending emails.

I think you already know how to do this: But (on desktop) go to thunderbird-> Account Settings -> (btm right) Edit SMTP Server. Then change the port and type to match the above:(port 465, SSL/TLS, Normal Password)

Let me know if this helped!

Thanks for the idea, though unfortunately that didn't help: tried 465 + SSL/TLS and got a server did not respond/could not be reached error (same with 465 + STARTTLS, though I'd assumed that wouldn't work anyway). Switching back to 587 + STARTTLS still gives timeouts as before.

OK, Thanks for the prompt reply.

Have you tried to reboot in Troubleshoot mode to see if an add-on might be causing the issue? Always a good idea to rule this one out.

Thanks likewise - just tried that, but sadly no luck there either: I was only running one add-on in any case.

Thanks for your prompt replies James.

Please try the following if you haven't already:

1. Please try removing the add-on. Generally, Thunderbird Troubleshoot mode works but sometimes it doesn't! 2. Please try disabling all 3rd party software including anti-virus (often anti-virus blocks Thunderbird updates) as you probably know but can't hurt to try. (I know you tried disabling the firewall) 3. " work runs an Outlook/Microsoft mail server" <-- Have you tried filing a support request with your Microsoft admin? Microsoft runs a diversity :-) of email servers and can often change them unpredictably without warning which can result in SMTP i.e. sending email failing.

Cheers! ...Roland

I know this thread is a few months old, but I suddenly started getting the dreaded SMTP server timeout error today using TB143.0.1 while trying to send an email. Only one of my Gmail accounts is affected. It can still receive emails (POP3) but can't send them. My other accounts send/receive without problems. Tried loading TB in Troubleshooting mode, but the problem with this account persisted.

My accounts use these SMTP settings: Server Type: SMTP Outgoing Server Server Name: smtp.gmail.com Port: 587

I changed the port to 465 and attempted to send that email from the problem account. Gmail asked me to log in and give TB permission to access the account, which I did, and then the email could be sent.

If I changed the port to 465, why didn't any of my other accounts make me log into Gmail and give TB permission? Any ideas why 587 stopped working for that one account, but not the others?

What am I missing here? Thx!