Since you searched for the file on the hard drive and found what you did, your best bet is to see if you have backups from prior years because you have shown that they are not on your computer.

I don't think you understand my problem.... The problem is the forwarding filter works just fine and I need to stop it, but I don't know where to find it or how to stop it. I do use a global password, so that might have some impact.

BTW: I have upgraded to version 115.12.2

One possibility is to just rename all of the msgfilterrules.dat files with Thunderbird not running to see if they are involved. Also, check your sent folder to verify that you're forwarding them and not from somewhere else.

I ran AgentRansack on my full HDD looking for any files named msgfilterrules.dat and found quite a few (not a surprising amount considering the # of accts changes I have made). I looked at all of them associated with the email provider in question and found that each one had the 2 lines I noted above, so i don't see how the msgfilterrules.dat files are doing anything.

I also tried searching in "C:\Users\<user name>\AppData\Roaming\Thunderbird\Profiles\<profile name>" for any files containing the name of the target account that is receiving forwarded emails. That produced a list of all the message files that contained messages, but I didn't see anything that looked like a rule. I am currently trying again with the sender name that is in the rule because there should be many fewer instances of that, but I doubt the outcome will be much different.

It looks to me like the rules are being stored someplace else, but I am not finding where. Would be nice if one of the developers would jump in with some info.

Just as a sanity check, exit thunderbird and check mail online to see if the mail is still being forwarded. That should either confirm that this is happening by Thunerbird or not.

It is pretty clear the forward is happening in TBird. The time stamp on the forwarded email corresponds with when I open TBird, even though the original email was sent by the originator in the middle of the night. To be clear: the delay is expected and not the problem. The problem is that the account the email is being forwarded to should no long get the email.

After many google searches, everything I have read about the filters makes it sound like msgFilterRules.dat contains all of the filter information. IT DOES NOT! Nor does Tools>Message Filters provide anyway to Edit filters.....even though that is what the documentation says. This is the type of misleading info I expect from MS and why I switched to Mozilla in the fist place. If someone from Mozilla doesn't step in with accurate info, my next step is probably going to be evaluating other email clients.

First, this is a peer-to-peer forum and your threatening to quit thunderbird if you don't get better free support is offensive. Only 1% of users donate and many those are the type who donate $10 once in a lifetime and think they're being generous. You can switch to Posbox with only minor conversion options an only for a lifetime subscription. TheBat is a good email client, but has high conversion requirements and you'll be paying $40 or more every couple of years for support.

Second, if you post screenshots of the filter inside the filter editor, someone may see the problem.