Go to Tools? Message Filters and see if you have any. You don't happen to have an addon like Mail Redirect do you? I also have multiple email accounts in TB and do not have this issue.

And that's where I went first. Only filter is Spam Assassin.

Thanks. The search continues.

outlook client anymore.

It turns out Outlook was still running in the background - I thought I had deleted it. But I checked message rules, and it was empty. No forwarding. I would delete Outlook but it has emails from 2018, which is probably why I didn't delete it. The old computer had all emails going back to 2013, but I couldn't get them to transfer. Am I being a little obsessive about hanging on to old e-mails? I've never really had to go back much to check on emails, so I guess I should delete them. But when I do, someone will ask.

Checked my e-mail server. Not as transparent, and I need to check further, but no rules readily visible.

So I guess I'm still a bit stumped on this.

PST to TB programs (just do as a free trial) and once you get all of your old emails then forget Outlook. I used Outlook at work with an Exchange Server and did keep a lot of my old emails like this for a while. After a few years I finally deleted but the address book came in very handy.

As far as forwarding of the emails that has me stumped. Are you saying that you have 3 separate distinct email addresses now set up in TB? Which email is forwarding to which other email? I don't understand.

Three accounts in TB - 2 personal and 1 business.

The business email is being forwarded to one of the personal emails. (I started doing that a few years ago for a reason that I can't recall.)

I did try to transfer the .pst files first to Outlook and then to TB. No luck in either case. The hard drive from the older computer stopped booting up about a month ago, but I still have it so that I can access files that I didn't transfer when I first got the new comptuer, including the .pst files. (I think I got most of the files I needed/wanted, so it's not a train smash if I can't access either the .pst files or any others for that matter.)

If I can save the .pst file from the working copy of Outlook (that I thought I had deleted but didn't), I will just delete outlook and see if that resolves the problem.

If it does, problem solved.

If it doesn't, I'll check with the company that hosts my business email, GoDaddy, and see if we can identify any forwarding.

And if the forwarding isn't there, I may just use a different email app for my personal email, and separate the business and personal emails that way. Maybe.

Thanks for your help.

Granted, first world problems, and not critical, but the annoying stuff is, well, it's damned annoying.

I've had a lot of weird things happen over the years, but not that one. Nothing fatal, but at times annoying.

But, digging around the help menus will get you to: https://support.mozilla.org/en-US/products/thunderbird

I've gotten quick responses to questions, but a lot of those responses were "We're working on that".

The good news is that almost anything you want to do you can do with it, and it is rock solid.