Is there an original as well as the numbered files? They are usually created when Thunderbird can not open the original file. Streaming backups and trying to sync the profile to the cloud are the common reasons files are unavailable on Linux machines. Anti virus takes the cap on Windows for the most common contention cause.

On a stable system there should be no files with a number on the end. There existence indicates something is broken.

Do you ever compact to allow Thunderbird to free unused space in the files? and shrink them

Thanks for the information.

For every file that ends in -1 there is a file with the same name which is much smaller than ends in .msf.

For example, Sent-2 is 8 GB while Sent-2.msf is 19 MB.

I don't recall ever having compacted files. Should I? Or is this what caused the -1 and -2 issues?

So what are my next steps?

Lets start with a compact. It is on the file menu (alt+F)

I doubt it will do anything to remove the numbered files, but it may significantly reduce the size of them.

Do these files show up in the Thunderbird user interface as having those same numbers?

I have a combination of IMAP and POP mailboxes.

The IMAP numbers do not show in the TB interface. Just the folder name: e.g. "Examples".

For POP mailboxes, I don't have numbers when checking with the terminal. I have the folder name and then an .msf file. For example: "Project" (100 MB) and "Project.msf" (10MB). The TB user interface just shows the folder name.

I have tried the compact but it does not reduce the file size at all.