Throttling pop3-login connections

[Alex]

Hi,

I have a fedora20 system with dovecot-2.2.13 running various services,
including pop3. I'm noticing some users are frequently hamming pop3, and
wondered if this was normal, or something I should be investigating?

Aug  8 14:05:20 email dovecot: pop3-login: Login: user=<user1>,
method=PLAIN, rip=97.77.115.121, lip=192.168.1.1, mpid=30509,
session=<DnRtDCIAUQBhTXN5>
Aug  8 14:05:21 email dovecot: pop3(user1): Disconnected: Logged out
top=0/0, retr=0/0, del=0/15, size=5693601

So it is immediately followed by a logout, but when there are 50 of them
successively in a five minute period, I wondered if it is creating
unnecessary overhead on the system?

I suppose this most likely is how they have their email client configured,
but wondered if some throttling would be necessary?

Any advice would be most appreciated.
Thanks,
Alex