Are you using smtp.centurylink.net on port 587 with STARTTLS security, normal password authentication, and your email address for the user name?

http://internethelp.centurylink.com/internethelp/email-setup-in-thunderbird-1.html#

Do you have a security program scanning outgoing mail?

sfhowes said

Are you using smtp.centurylink.net on port 587 with STARTTLS security, normal password authentication, and your email address for the user name? http://internethelp.centurylink.com/internethelp/email-setup-in-thunderbird-1.html# Do you have a security program scanning outgoing mail?

My settings in Thunderbird are correct per CenturyLink guidelines. I have been using Avast Free Version for at lease a year with no problems. With my current problem, I have disabled its "shield" several times which has made no difference. I don't know if it is scanning my outgoing mail.

I can ping and traceroute to that smtp server, so it is up and running.

Try starting your computer in its Safe Mode. This should disable the anti virus and thereby show if that is what is causing the problem.

https://duckduckgo.com/?q=windows+safe+mode+with+networking&ia=web

As mentioned above, running in Windows safe mode is the best way to see if AV is the problem. It wouldn't be necessary to disable the real-time background monitoring of Avast, but you might have to disable the 'Mail Shield'.

https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#AVAST

Using safe mode didn't solve my problem. Emails still cannot be sent out.

Zenos said

I can ping and traceroute to that smtp server, so it is up and running. Try starting your computer in its Safe Mode. This should disable the anti virus and thereby show if that is what is causing the problem. https://duckduckgo.com/?q=windows+safe+mode+with+networking&ia=web

Using safe mode did nothing to solve my problem. I still cannot send emails out and still receive the same message. "smtp.centurylink.net is unknown" even though it was recognized up until 3 weeks ago.

Select Windows key+R, type cmd, click OK, then type: ping smtp.centurylink.net

What do you see for the IP address, i.e the string that looks like:

Ping statistics for 206.152.134.66

sfhowes said

Select Windows key+R, type cmd, click OK, then type: ping smtp.centurylink.net What do you see for the IP address, i.e the string that looks like: Ping statistics for 206.152.134.66

I see: Pinging mail.onyx.syn-alias.com (206.152.134.66) with 32 bytes of data. Reply from 206.152.134.66: bytes=32 time=82ms TTL=245 Reply from 206.152.134.66: bytes=32 time=84ms TTL=245 Reply from 206.152.134.66: bytes=32 time=85ms TTL=245

That's the same as here. I had thought your computer might be resolving the server to an obsolete DNS entry, in which case it can be fixed by the ipconfig.exe /flushdns command. Still, it wouldn't hurt to restart your modem/router; it has fixed similar problems before.

sfhowes said

That's the same as here. I had thought your computer might be resolving the server to an obsolete DNS entry, in which case it can be fixed by the ipconfig.exe /flushdns command. Still, it wouldn't hurt to restart your modem/router; it has fixed similar problems before.

I restarted my modem, ran Privazer & CCleaner and rebooted my computer all with no success.

I'm not familiar with Privazer, but based on many issues on this forum with CCLeaner, I would recommend you check that it is not performing any 'cleaning' of TB. Not saying that is definitely causing the problem, but it's highly suspicious.

sfhowes said

I'm not familiar with Privazer, but based on many issues on this forum with CCLeaner, I would recommend you check that it is not performing any 'cleaning' of TB. Not saying that is definitely causing the problem, but it's highly suspicious.

Thanks muchly. I will check that aspect . I'll just about anything at this point.