Still having issues? I ask because often these sorts of issues are transitory

Thanks for asking. Can you say more what you mean?

My issues have not been transitory. After spending hours piecing together my best back up copy, items were disappeared again, from 2 of the 4 folders that had been emptied. And losing 100s of messages for good, even if it only happened once, is not something I would call transitory! It's painful!!! It does not seem like anyone else has had this problem though. I hate being so special.

Thank you for checking!

What is your anti-virus software?

Avast, same as it's been for years.

Thanks for your interest.

See http://kb.mozillazine.org/Disappearing_mail

A common cause for lost messages is anti-virus software messing with Thunderbird mail files.

Create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Don't let your anti-virus software scan incoming and outgoing messages.

Don't let your anti-virus software scan attachments.

Don't let your anti-virus software intercept your secure connection to the server.

Remove any add-ons your anti-virus software may have installed in Thunderbird.

Keep it working. http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

Specifically for Avast: https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#AVAST

Jesus, thank you. That was helpful. I would say that I now know that I have a corruption issue. I did the "rebuild from within Tbird" technique & maybe that will solve it. If not, I am not sure what to do, because it sounds like corruption is an issue of noncompacting, & I have always had frequent automatic compacting, have not kept a lot in the inbox.

I have huge folders. The profile backup is 2 gb, not many attachments, just 1000s of messages. I don't know if that is the problem & what to do about it.

Thank you.

Take a look at the archive feature. https://support.mozilla.org/en-US/kb/archived-messages

Looks like moving emails out of the inbox to dedicated folders as I do is as good as archiving in some ways:

http://forums.mozillazine.org/viewtopic.php?f=39&t=2406719

But I bet my performance would improve with fewer emails within active folders in Tbird:

http://www.ghacks.net/2010/09/17/how-to-speed-up-thunderbird-by-archiving-emails/

Mostly the emails I keep are ones I access, but there are some that I access infrequently.

Thank you for that idea!

Looks like moving emails out of the inbox to dedicated folders as I do is as good as archiving in some ways

This is essentially what archiving does. Basically the idea is to break up large folders in to smaller pieces.

But I bet my performance would improve with fewer emails within active folders in Tbird

What's primarily slowing down Thunderbird is anti-virus software trying to scan large email files which are frequently accessed, like Inbox, and Sent.

Are any of these accounts were message are disappearing IMAP accounts

Hi, Matt with beautiful facial hair. I have 1 account with some subfolders in the IMAP inbox and some POPped. I have had some of each disappear.

I watched some IMAP ones disappear again. I saw 57 emails listed in the subfolder, but only 3 were showing. Then it said it was deleting 54. Then it said 3. I closed & reopened TBird several times & finally the 57 reappeared. It happened with another subfolder soon after, with 75 emails disappearing & eventually reappearing.

My folders that I move emails into many times a day are not small. They are POP folders with 1000s of emails.

I read the Avast info. I turned off outgoing scanning, but prefer to have incoming scanning on. I am not sure that that solved anything.

Your thoughts?