Since upgrading to Big Sur, Mail is a mess. Can't move email to other mailboxes. They just disappear!

POP disappearance can happen because the Spotlight index is incomplete. Go to Apple menu -> System Preferences -> Spotlight, and add and remove the hard drive from the privacy section.

You can then look in the Spotlight menu to see if you are still indexing.

Do not use any optimizers, cleaners, Mackeeper, or any such software. These can cause apparent file loss, and prevent the system from properly launching. Use Etrecheck, and we can probably help you diagnose what may be installed that is preventing your system from properly portraying your mail:

https://discussions.apple.com/docs/DOC-250002463

Have you installed or run any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac?

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

I too am having the same problem. This problem has only occurred since the last os upgrade. eMails appear in my Inbox ok but as soon as I try to move them to a folder in my eMail filing system, the eMail vanishes. The problem is frustrating because this is happening on my primary device, a macBook Pro. If I then try to access Mail on my iPad, initially the eMail that are lost, then they immediately vanish. Where have they disappeared to and why have they vanished. I am trying to resolve this situation. I had re-installed Big Sur. What I feel is that I may have to re-install Mail. Some help, please. thank you

As stated previously, if I try to drag and drop an eMail from the Inbox, the eMail being dragged just disappears.

I have re-installed Big Sur but I am having to resort to using the 'Copy to' menu feature to sort my eMails. This makes it a real pfaff to sort and save my eMails.

This action "disappearing eMails" is a reasonably new manifestation, since about the time of updating to 11.5.1 (only a day or so after the 11.5 update), but maybe this is a coincidence.

I had noticed some previously flakey action when dragging and dropping eMails. For instance, clicking on the eMail sometimes turns the line blue and the item is dragged and dropped as a "blue line". Other times, clicking the eMail causes the line to morph to an envelope icon. This might or might not be connected. Either way, it is not the rock solid consistency that I have become accustomed to with my macBook Pro.

Are you using IMAP, POP, or exchange?

How big is your hard drive, and how full is it?

I am having the same problem--unable to move an email to a specific mailbox in BigSur. The email disappears. I followed the steps and got no corrective results. What next? Thanks.