What are your settings ? Try mine

Checked my settings they are exactly the same as yours. Except for the user name of course

Try Run TB in safe mode

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

I've already tried disabling my antivirus and that didn't affect anything or help. I'll try safe mode.

How experienced are you? Can you make and run a cmd file? If so you can make this file, it temporary set some logging variables and starts TB. The varibles will be reset when you exit TB. I assume you are running Windows 64bit? Otherwise you need to change %Programfiles(x86)% to %Programfiles%

set NSPR_LOG_MODULES=smtp:5 set NSPR_LOG_FILE=%USERPROFILE%\Desktop\smtp.log "%ProgramFiles(x86)%\Mozilla Thunderbird\thunderbird.exe"

Just start TB with it, send something and quit. And you should have a smtp.log on your desktop, examine it

Edit The cmd-file must have the extension: .cmd

I'm pretty experienced - worked IT for 20 years. I'll try that batch file. Just an FYI. I deleted the TB profile in my %AppData% and re setup Thunderbird. Attachments worked again for a while briefly but now I'm back to that problem where they won't send again and it times out.

in the log file what would I be looking for that would be potential problems?

I cant tell but Look for an error, first that the connection and authorization is accepted. Send: From ... and To ... get OK Send DATA#### (DATA+ number) get Go ahead .... Send .#### (a point+number) get OK (end of Data) Send QUIT#### get closing connection ..... .... The last line would be connection error quitting ......., ignored

How did safe mode do? (btw I also worked many years in IT, now retired)