What is your anti-virus software?

christ1 said

What is your anti-virus software?

Zone Alarm, but it does the same thing, even if I turn it off.

Try to start *Windows* in safe mode with networking enabled.

- Win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode

Still in Windows safe mode, start Thunderbird in safe mode.

- https://support.mozilla.org/en-US/kb/safe-mode

Does the problem go away?

In safe mode, it behaves properly. ie problem goes away.

christ1 said

Try to start *Windows* in safe mode with networking enabled. - Win7 http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/en-US/kb/safe-mode Does the problem go away?

In Windows safe mode anti-virus software is disabled. So that indicates your problem is with Zone Alarm.

Don't let it scan your Thunderbird profile folder, i.e. create an exception for the profile folder. Don't let it scan attachments. Don't let it scan incoming and outgoing messages. Remove any extensions it may have installed in Thunderbird.

You may also ask in a Zone Alarm forum.

I uninstalled zone alarm and it still does it.

What other 'security' software are you running?

None at all

If you have Windows OS then you may have Microsoft Security Essentials auto running.

Running win7 but looked at uninstall programs in control panel and don't see Security Essentials anywhere.

It is also possible you have 'Defender' running which is an anti spyware product prior to windows 8.

Look in the 'Control Panel', perhaps here: Control Panel > System and Security > Action center

Action Center manages firewall settings, Windows Update, antispyware software settings, Internet security, and User Account control settings. so it should be able to tell you what is running.

the only thing listed there is zone alarm (I reinstalled it)