The error is coming from a glinx server. Are you trying to send from an xplornet account or a glinx account? The glinx smtp must use STARTTLS security on port 587.

I am sending from a Glinx account that uses STARTTLS and port 587.

Timeouts are often caused by antivirus programs that scan outgoing mail. What is your AV, and is the TB profile excluded from scanning, the generally recommended setup?

I'm using Norton antivirus and don't want to exclude TB from the scans. I can use my cell phone as a wifi hotspot and the TB emails go out fine with no error message. My cell provider is Eastlink.

Do you know if TB maintains a database of emails and ip addresses to confirm the emails are coming from the correct user?

If you want to test if Norton is causing timeouts, run Windows in safe mode, which bypasses startup apps.

http://kb.mozillazine.org/Antivirus_software

I don't think there's a database, but your incoming accounts should be matched with outgoing servers with the same User Names, e.g. the glinx account sends on the glinx smtp, the xplornet account sends on the xplornet smtp etc.

Interestingly, my computer running in safe mode does not recognize the Xplorenet wifi networks available. Pressing F4 or F5 at the restart option, I get the message that I'm not connected to the internet. But when I restart normally the computer recognizes the two networks.

I really don't think Thunderbird is my problem. I get a similar outgoing server error message on my wife's Ipad, only the Ipad will eventually send the message.

So, what do you know. I can send email again. Seems to have fixed itself. Perhaps all the restarting I tried reset something?