I should add that I've been running this setup for 2+ years and this issue just started after a software update last weekend.

Update. It turns out it's mainly (so far) just one of my project mail folders that I can't move messages into, it just so happens to be my current project. I am able to move messages from my inbox to a number of other folders. I created a new folder for the project and can move messages into it.

I also discovered that attempts to drag-n-drop into the problematic folder does not "lock-up" my inbox, but if I use either the RMB menu or the file menu to try to move messages into that problematic folder, that is what locks-up my inbox causing me to have to close and reopen Tbird.

I tried doing a "repair" on the problematic folder, no change.

where is this folder located? on a network or attached drive? A cloud synced or other streaming location?

BTW I don't play with Linux any longer, but I have no idea what the RMB menu is and I have no message move functions on my Windows file menu. I assume Google got it right and the RMB menu is the context menu.

I would suggest checking that you have write access to the relevant folder at the operating system level. If the issue takes days to evolve, it sounds like the system may be loosing the pointer to the drive. This might be because the file is on a network, or is cloud based. Where is the file physically stored?

you might want to try accessing the error console, clearing it and then trying you copy/move and see if the issue present anything useful in the way of errors. before things lock up.

The Copy and Move both require a round trip to the server for IMAP accounts (the default so I will assume it). First to confirm the local copy ios the latest, then again to notify the server of the status change in the current folder and in some cases another trip to another IMAP server to notify the creation of a new email in the account. All of this follows the thread of lost connectivity either to the server or the disk being the underlying cause. Hopefully you can turn up something in the error console.

Thanks for the reply Matt. Yes, RMB is Right Mouse Button. We use that at work all the time, I guess I thought that was a standard abbreviation. All of my mail folders are local. So Tbird on Windows uses a Ribbon UI? I'm very happy that most Linux apps stayed with drop-down menu structure and didn't go the Ribbon route, which I find wildly inefficient.

I am not using IMAP, I'm using POP/SMTP. I often work in environments with no internet and prefer my email does a quick sync whenever my laptop can catch a signal.

I haven't used the error console, but from a quick search it looks like it could be helpful. Though I'll have to figure out how to invoke it as it doesn't exist in my version of Tbird where others have indicated.

Hi Matt: re: I have no message move functions on my Windows file menu.

I see it on my version. On 'Menu Bar' toolbar....'Message' > 'Move to'

I also still use the Menu Bar toolbar as it's just so much quicker etc etc etc.

I agree with Matt, it sounds almost like the mbox file has a read only setting. Help > More TRoubleshooting Information Under 'Application Basics' half way - Profile Folders - click on 'Open Directory'

A new window should open showing all the contents of your profile name folder.

Exit Thunderbird now.

click on 'Mail' folder click on pop mail account name folder

locate the mbox file (no extension) that has same name as the folder which is not receiving mail. If it's a subfolder then it may be located in a *.sbd folder.

Right click on mbox file and select 'Properties' check the 'Attributes' - is 'read only' selected ? If yes, then uncheck that checkbox. check the 'Security' tab to see if you have all the required permissions to Write, Modify etc.

Thanks for the reply.

Somehow Tbird is using Handbrake as the default application to open the profile folder which doesn't work too well, but I know where the profile folder is and navigated to it using Caja. Unfortunately the folder settings look good, it is set to read/write and my user is the owner. I compared the properties with the new project folder I made and have been using, they are the same. The problem folder is rather large, 247 MB, but I have another from a previous project that spanned 2 years that is 975 MB and I can still move messages into that one.

Recently, when I "move" email messages from my Inbox to another subfolder which I created under "Local Folders," the email initially DOES move. And then it reappears in the inbox and shows that I never moved it. This has happened multiple times. I have restarted, makes no difference. Also happens when I go to "Sent" email: when I try to move messages there to another subfolder, initially it works, but then moving back to "Sent" mail, the original email which I had just moved shows up again. Anyone help?