Sign in doesn't work

this has happened to me several times for several days each time. eM Client refuses to sign in to the server (saying the server doesn’t recognize the sign in details) - despite my email address and password being correct. The server is working because I can get in on webmail for that ISP with the same sign-in details. After several days the problem seems to clear of its own accord. I am wondering if I uninstall eM Client and reinstall will it preserve all my stored emails (there are a lot). I have made a backup using em Client’s back up but there is no obvious restore and I have no idea where the backup lives on my PC.