Issue Timed out on port 143 and 993 when managing mails on my server

[LaurentR2D2]

Plesk Obsidian
Centos 7

Hello,
Since several days, I can't do anything on my mails, like deleting them, moving them from one folder to another, without having a timed out. I connect to my server with IMAP. I've changed nothing on it, besides installing Plesk Mail Premium without activating it on any domain for the moment. So I wonder if this problem is a software problem to check on my server, or a problem with the server itself. I've contacted the company who rent me this server, but I have no answer from them for the moment.

Thank you