Error Console shows bugs in the update

It is possible your Firewall is blocking Thunderbird's access to internet. Maybe the Firewall thinks the update is a new app. I've known Norton to get this wrong in the past.

The Firewall may be one packaged as default with computer or part of your Anti-Virus product.

Exit Thunderbird. Access Firewall

Thunderbird must be an allowed program. If it is not in the list then add it. It it is in the list, then block it, ok it - then access Firewall again and allow it and ok it. Start Thunderbird.

Also: If the Firewall got an update maybe it has switched on a 'VPN' setting. Norton 360 did that to me and caused more problems than it was worth not just in Thunderbird but when I clicked on known specific links it was sending me to websites that were not remotely where I wanted to be. Access Firewall and switch off any VPN setting.

In addition: Running two anti-virus scanners at the same time will ultimately cause problems. Check - are you allowing two Anti-Virus to run symultaneously ? Ideally, don't let your anti-virus software scan the Thunderbird profile folder. Don't let it scan incoming and outgoing messages. Don't let it scan email attachments. Or if you do allow this - then please do not allow an auto fix, it must tell you so you are aware of it, but never let an Anti-Virus or Malware program attempt to fix anything to do with Thunderbird.

Thanks - my firewall is disabled. Only one anti-virus.

And no, I wouldn't touch Norton with a bargepole ;)

And as I said - no system settings have changed - this was not a Windows update, only Thunderbird from 91.8.0 to 91.8.1.

Up until this morning's auto-update, Thunderbird has been running fine for many years.

Can I possibly download an older build, or roll back this update?

Can I download previous builds somewhere?

re - my firewall is disabled. Only one anti-virus.

Do you mean the Windows 10 default Firewall is disabled? So is mine, but I'm not allowing my computer to be wide open to attack, I do have the Anti-Virus operating the Firewall.

It's not just Norton which throws a wobbler when Thunderbird gets updated.

I'm not talking about AV or OS getting update. It's all about how they react to a Thunderbird update and you had a Thunderbird update. If nothing is going in or out then it is being blocked.

What Anti-Virus are you using? Is the Anti-Virus running the Firewall ?

Downgrading can be done but it's not exactly straight forward like it used to be.

Thanks,

I have Avast Anitivirus. Windows defender firewall is disabled, yes.

Outgoing mail is actually going out - but all three accounts set up in Thunderbird haven't received any email for the last 3 horus - and through webmail I see that there are new messages today.

When you say rolling back is no loger straightforward - what do you mean - how do I roll back correctly? I have found a folder with older builds in the meantime.

Thank you again! Appreciate it.

After another restart or two - Thunderbird decided to work again and is receiving incoming messages.

Rollback to the earlier build did the trick.

Thanks again for your help @Toad-Hall !