I assume the correct option is selected in the anti spam toolbar part of web and email protection?
I would call support as they need to know the version/build of mcafee and the thunderbird build. Better to nip this in the bud than 1 month down the track
Thunderbird version is 17.
Security Center: 12.1
Personal Firewall: 13.1
Parental Control: 13.6
Anyway, I found in some discussions that it was due to real time scanning when "scan attachments to email" was selected. So I just deselected this option, and it is working fine again.
It was not when sending/receiving emails, it was just a permanent lock of thunderbird that made it totally useless.
Thank you for your replies.
I've given up on McAfee. I'd rather have Thunderbird working correctly and then have something else for virus protection.
I'd installed McAfee Total Protection twice, set it to not scan email attacvhments and not to automatically update. This worked fine.
Today, McAfee popped up and said a PROGRAM update was installed please reboot. At this point I didn't have any choice. Eventually I would need to turn off the computer and restart it.
I did, and the newer type user interface (with the squares) instead of the old (section in columns) appeared. And Thunderbird jammed up and quit working again.
I used Add/Remove programs to remove McAfee and then used MCPR.exe to completely remove McAfee.
Thunderbird now worked correctly.
I installed Microsoft Security Essentials.
I have a 3-computer McAfee installation and have it installed on another computer plus a laptop. I'll leave it running on these computers, since I don't use Thunderbird on them. I just renewed it for a year, so I have a while to make a decision about what to use when renewal comes up again.
Rumor has it that McAfee is aware of this problem and promises a fix by the end of the 1st quarter of 2013. I'll wait until I see some further information.