My personal opinion is McAfee is the most malicious software you have.

without details of exactly what the files contained a wild guess is the best you can hope for. One thing I do know is that what these products report as malicious is frequently not at all. Why do you have files numbered up around 100 if you are going to use McAfee you might want to manually clean out your system temp folder as it is full of junk.

If you change the Thunderbird configuration to not allow antivirus products to scan new emails those files will not even be created they exist only so the antivirus can eliminate malware before is is stored with all your other mail and the attendant disaster the flailing of the antivirus product in deleting all the mail in the folder can start.

Hey Matt, Thanks for your response although IMHO I think your opinion of McAfee is a bit OTT! I consider it no better or worse than any other AV although your sentiments are noted. You will be glad to know after I contacted McAfee support when I received these alerts ... I uninstalled their software ;-)

I clear .tmp files from multiple laptops on a regular basis. Those 2 were the only ones in %temp% today. This laptop is 6 months old, and came pre-installed with McAfee. I installed Thunderbird the same day and is my only email application.

Today is the first time I've seen these. What got my attention was the fact that my version required multiple updates when I have it set to "Check for updates, but let me choose whether to install them".

So I was curious to know what generates these newmsg files, are these new, and being too lazy to read all the release notes, will the latest versions still generate them.

Nothing new about them at all. They are attached to the "allow antivirus products to scan for virus setting".

It goes back to about V2 I think.

I felt due warning of my bias re McAfee might be relevant, but there is a little documentation to support that in general here https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues. I feel similarly about Norton because neither product has actually improved in the last decade, instead of providing quality efficient products, they use fear as their selling and retention points and spread the invasiveness of their software ever deeper into the operating system internals. Little better than ransomware I feel.