Frequency Control for IMAP connection

Hello

one of our users makes too quick IMAP connections to the server.

$ sudo tail -10000 /var/log/mail.log|grep **@**mail.com|wc -l 3544

logs like this:

Aug 15 19:54:10 mx dovecot: imap-login: Login: user=<**@**mail.com>, method=PLAIN, rip=**, lip=**, mpid=4151830, TLS, session=<UPotgLcfTOjYUzTN>

How can I implement a Frequency Control on client connections to slow down his requests?

Thank you.