connecting with IMAP stopped working

Hi,
I have Ispconfig 3.2.9p1 installed. Today, since noon, My Email client Outlook and IOS devices can't connect to the IMAP server. Webmail/Roundcube is working fine. I'm getting there new email since noon, and I can also send emails.

I was checking the mail.log in ISPconfig.
Aug 25 15:28:04 ns1 dovecot: imap-login: Login: user=<XXX>, method=PLAIN, rip=::1, lip=::1, mpid=6896, secured, session=<WDp9UL8DpKcAAAAAAAAAAAAAAAAAAAAB>
Aug 25 15:28:04 ns1 dovecot: imap(XXX)<6896><WDp9UL8DpKcAAAAAAAAAAAAAAAAAAAAB>: Logged out in=92 out=983 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0
Aug 25 15:29:05 ns1 dovecot: imap-login: Login: user=<XXX>, method=PLAIN, rip=::1, lip=::1, mpid=6949, secured, session=<3cEcVL8DHIQAAAAAAAAAAAAAAAAAAAAB>
Aug 25 15:29:05 ns1 dovecot: imap(XXXX)<6949><3cEcVL8DHIQAAAAAAAAAAAAAAAAAAAAB>: Logged out in=92 out=983 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0

I redacted the user to XXX - user is OK. Showing the correct email user name

I have no idea what is wrong. Mail Errog log is empty in ISPconfig.

I ckecked and my SSL certificate didn't expire today. It is still valid until mid September.

Any idea please?

 

Please disregard my problem. It is a problem with internal network.