Just wondering something. On Windows* (at least this was the case decades ago) if you uninstalled then reinstalled a misbehaving program all the settings stayed in place. Does the same work with an email client on Linux? And is that even worth trying, more to the point?
I think it does retain all settings. At least on Debian and claws mail. I seem to remember having to do a complete system reinstall, and just kept my home folder untouched, and everything worked fine on restart. I don't recall any more whether I had to point claws to the files again, don't think so.
You can make completely safe by backing up the settings and mail files, and I would. Then if they do get overwritten during the resinstall you just copy them back. I have done this on Debian with claws when making a laptop in sync with a desktop. Just installed claws, then overwrote the new files it had created with the corresponding desktop ones, and all the files and settings were there just as on the desktop.
Safest to back up first, why risk it.
Is it worth doing? Don't know. I would be inclined first to try with another email client and see if it happens with that. I really like claws, its light and fast and it will handle many thousands of emails locally with no problem. At least that would tell you whether its the client or something common to both of them. Though I can't really imagine what that would be!
Peter