For months people have been reporting strange problems with Mozilla’s Thunderbird e-mail client. I have maintained that the problem is not likely to be Thunderbird, but is more likely to be related to a user’s ISP or a Windows issue or a firewall blocking access. I think I have found and verified at least one potential source for the ongoing issue with either inbound or outbound mail becoming disabled.

Almost a week ago I upgraded my main PC with a new hard drive. This included a re-installation of Windows XP and all of the software. I had been using Norton Anti-Virus 2008 on the old hard drive, but have heard good things about the new version of Norton Internet Security 2009, so I installed that on the PC. I have not used Internet Security in the past because it was known for being a resources hog. Symantec claims to have resolved these issues, so it was worth a test drive.

Symantec seems to be updating their virus definitions more often these days due to increasing e-mail attacks. I get a lot of e-mail and it has been catching 50 to 10 viruses every day. A few days ago, Thunderbird e-mail ceased to function for the e-mail accounts on my server as well as my Cox accounts. The problem seemed to go away as I was installing software and rebooting the PC.

Today, both incoming and outgoing e-mail ceased to function in the afternoon, but it had been working well all morning. My AT&T accounts were still working with Thunderbird, but Thunderbird failed to either send or retrieve e-mail from my mail server and my Cox account mail server. I further found that I could not access my web server cPanel accounts even though the web sites were still working properly.

I suspected that the Norton firewall was blocking access to the ports on my server that allow access to e-mail and cPanel. I opened up Norton and immediately noticed that the virus definitions had updated a few minutes ago. I also noticed that under Internet Settings the Anti-Virus controls were turned off and Norton would not allow me to turn it back on.

At that point I didn’t know if a virus had gotten through and disabled Norton. That did occasionally happen several years ago. I rebooted the PC and found that the Anti-Virus controls were back on an I could once again send and retrieve my e-mail. When I downloaded my backlog of e-mail, Norton did find and disable another nasty virus from some script kiddie hacker. I could also access cPanel on my web sites. Son-of-a-gun!

Here is what I suspect is happening

I suspect that when certain types of virus definitions or program updates are automatically downloaded, Norton is disabling the Anti-Virus controls until the PC is rebooted and the updates are loaded or installed properly. Along with that, it is disabling certain server ports to prevent someone from accessing a server where they might pick up a virus when the anti-virus checking is disabled. AT&T e-mail uses SSL encryption, so it uses different server ports than those used by standard e-mail. That might explain why AT&T e-mail continued to work.

That leads me to the conclusion that the disabling of e-mail access by Norton is probably intentional, but they are not displaying a message advising you to reboot the PC.

I have not found any information about this issue on the Symantec web site and I have learned from past experience that trying to resolve an issue through Symantec’s technical support is worse than useless.

Let us know if rebooting your PC resolves your issues when Thunderbird mysteriously stops working.