I currently use McAfee, but I'm changing over to Norton when I migrate to a new computer. My McAfee subscription on this computer expires on 6/24, hence the urgency to get through all my old e-mails by 6/22. Also, I changed my mind overnight. I'm going back into Thunderbird this morning in "normal" (not Safe) mode to: a) see if the problem comes back, and b) make sure I can still communicate with my internet service provider's (ISP's = Comcast's) e-mail servers and confirm that I can still send and receive e-mails after being in Safe mode. I'll let you know what happens.

I went back into Thunderbird after a "normal" re-start. Sending and receiving messages works fine, but the problem (having to empty trash and compact folders) came back immediately (on my first delete attempt). I am likely to reboot again in "Safe" mode as I continue to go through and delete e-mails. Once again, I will keep you informed.

Changed my mind. Continued to go through (and delete) e-mails while in "normal" mode so I could communicate with the outside world while I did it. So --- Safe mode may keep the error messages from coming up, but it's not really a solution to the problem. Who wants to work in Safe mode and be isolated from the rest of the world while you do it? Can't even receive or send e-mails while in Safe mode. I have a local area network with 3 computers and the other 2 couldn't talk to this one while I was in Safe mode. Also, I tried to open Microsoft Excel in Safe mode and that wouldn't work either. I think it's because Excel now has Help out on the internet instead of storing it on a user's hard disk.

Thanks for your help in testing safe mode and the continued updates.

Working in safe mode of course means some software which is running after windows startup is interfering with Thunderbird. Most likely your antivirus software. Setting an exclusion in the AV settings on the Thunderbird profile directory is the normal adjustment.

backup software is also known to cause issues.

I use McAfee on the computer where I store my e-mails. McAfee will not allow folder exceptions. I can only choose files, not folders, to be excluded. I just checked. There are 5,773 files in my Thunderbird Profile folder on this computer, which makes establishing McAfee exceptions impractical. I use Norton on another computer I have. I AM able to make an exception of the Thunderbird Profiles FOLDER on the computer using Norton (the Norton software allows folder exceptions). I also notice there are only 2 (TWO) files in the Thunderbird Profiles folder on my Norton computer. Further inspection on this (the computer where I'm having the problem) reveals an extra (Cache2) folder (in the Profiles folder) on this computer. This Cache2 folder DOES NOT EXIST on the other computer where I have Thunderbird installed. The Cache2 folder on this computer has a "doomed" subfolder (which is empty) and an "Entries" subfolder which contains 5,769 files! with a date range of 6/12/25 to 6/19/25 (today). The Thunderbird release on both computers is the same (128.11.1). All this tells me that Thunderbird is doing something that conflicts with other Windows applications and that the Thunderbird development team needs to identify what it is that Thunderbird software is doing that creates these conflicts. Let's put it another way: Microsoft Office applications operate with no conflicts with other antivirus (or backup) programs. What is Thunderbird doing that is incompatible with these other applications?

Let's put it another way: Microsoft Office applications operate with no conflicts with other antivirus (or backup) programs. What is Thunderbird doing that is incompatible with these other applications?

Fortunately, other apps don't have hundreds or thousands of user files that require real time access.

I don't personally have McAfee to verify this information, but https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#McAfee documents the possible exclusions that have worked in the past.

Wayne, Thanks for the McAfee link. I'll check it out. Those in the community should have that (and the Norton link) handy so people like me won't have to search for them.

You gave me an "Aha" moment (about real-time access to thousands of user files). Some (hopefully helpful) thoughts for the development team come to mind:

1) Contact the Microsoft Outlook development team. They must have a solution to this problem, or they have a structure that keeps them from having the problem. Buy a copy of Microsoft Outlook to see how they structure things.

2) I am a long-time (legacy) Thunderbird user. There was a time when this wasn't a problem (I could delete 100's of e-mails at a time without getting an error message). Something changed in Thunderbird's software. Finding out when this became a problem might be helpful in solving it.

3) Create a re-usable stress test that can be run prior to each release. My suggestions: Put 15,000 e-mails in the Inbox and 15,000 in the Sent folder, 10% with attachments and 10% with imbedded images. Try to delete 1,000 e-mails from each folder at a time in sequence until the folders are empty (without emptying Trash or compacting folders). Buy a copy of Microsoft Outlook and run this stress test against it if you think that would be helpful.

4) I heard this at a conference once: "If you have an unsolvable problem, give the job to someone who doesn't know it can't be done!"

Take care ---

Wayne, I checked out the McAfee link you sent.

1) The McAfee description of how to make McAfee ignore Thunderbird's profiles is inaccurate and not really usable. McAfee no longer allows folder exceptions (only file exceptions). I recommend someone modify the text by referring to: https://www.mcafee.com/support/s/article/000001661?language=en_US a McAfee support URL, which describes how to make file exceptions in McAfee.

2) The Norton section is accurate, but also not usable. I challenge the author to open either app (McAfee or Norton) cited at your link and find ""On-Access Scan properties ..." on either home page.

3) I use both products and know how to get to the sections that allow file exceptions in McAfee and folder/file exceptions in Norton, but haven't got the time to create a post for that. Maybe someone in the community could step up to the plate for that.

3) I disagree with the statement that issues between antivirus software and Thunderbird are the responsibility of the antivirus software provider. Thunderbird should be working with these antivirus providers to make sure they work with Thunderbird. On the flip-side of that coin, I do not think Thunderbird should be responsible for making sure Thunderbird works with EVERY antivirus product. I think McAfee, Norton, and possibly Windows Defender (the antivirus capability that comes with the Windows 11 operating system) is enough of a responsibility for Thunderbird. Just putting in my 2 cents here.

Thanks for all the info. I can update the docs. It is unfortunately, kind of absurd that they don't allow excluding folders, because they clearly are capable of providing it as they have done so in the past. You might try setting an exclusion on the Thunderbird executuable.

I have personally dealt with vendors in the past (in an non-coder capacity) on very technical issues on their interaction with Thunderbird - for example McAfee, twice. It is extremely time consuming, takes weeks and months sometimes for a resolution. In each case I spent 10-20 hours helping them connect to customers having problems, to help them solve their product's problem.

Also we can tell that vendors have special code or hooks to work properly, because (at least in the distant past) we'd get more user complaints when new version of Thunderbird came out, even though there was no change to the Thunderbird file IO code. So customer complaints to the vendor tend to have a bigger impact, which is why we encourage users to file tickets with the AV company.

Good news though, development of a new message database is well underway and expected to be available later this year.