I'm assuming it is a Gmail account, so try these instructions: https://www.supertechcrew.com/thunderbird-oauth2-gmail/ It fixed my problem.

Thanks, Sea Mac, but it's not Gmail, my email is with Netspace...

You need to check the outgoing server smtp settings are correct and also check whether the account is actually using the correct smtp server for that account. See images as a guide, so you what area I'm talking about. Obviously your server will be different.

Note: The 'Description' field is really useful to help you make sure you have selected the correct outgoing server for the account.

check the smtp server setting, ports , Connection Security is coorect as per your server requirements. 'Authentication Method: Normal Password' User Name = full email address.

For Netspace, use mail.iinet.net.au on port 587, STARTTLS security, authentication = normal password, User Name = email address.

https://iihelp.iinet.net.au/Email_Settings

If you already have those, check if there's a security app scanning outgoing mail, and disable that option, as it may have become incompatible with a TB update.

Thank you all for your replies. I'll try to fiddle with it later. I am not computer literate and I guess the main thing I don't understand is why the email settings went out of whack when I haven't touched anything. It looks like it has happened to other people too.

janeway said

Thank you all for your replies. I'll try to fiddle with it later. I am not computer literate and I guess the main thing I don't understand is why the email settings went out of whack when I haven't touched anything. It looks like it has happened to other people too.

There are usually two reasons. Which it is in your case is difficult to guess.

1. The settings required by the provider have changed. 2. You have software on your computer that is not working correctly. This is usually an anti virus / Internet security suite and it is quite common after an update to Thunderbird. Some like Norton products have a habit of blocking everything in their firewall component. Others like McAfee force feed an addon that is not compatible with the new version causing failures.

I do think I recall that iinet used to allow sending without authentication if you were connected to the internet using their service in some circumstances, but I also thought that went by the wayside about a decade ago.

Thank you, Matt