webmail and IMAP/POP servers are normally separate, but your account profile will be shared from a different server. If webmail works, it means your account profile if fine but something is stopping the IMAP/POP authentication. The password should nrmally be in sync between the servers but as always in networks things can go out of sync. So before anything, if one works and not the other, reset your password upto 3 attempts and only if that does not resolve your issue is elsewhere. I spent many months battling this issue for my partner before i found the workaround.
Thank you so much, you have saved me so much time and frustration, hope everyone else manages to resolve their issues too. Fingers crossed it behaves from now on
It won't. You would have been much better setting up an ISP independant email address such as Gmail.