[Dovecot] Is there a way to limit multiple POP3 connections?

[patrickm]

Hi all,

Please correct me if I'm going about this the wrong way.

We currently have a 3 system Mail server set up - two machines are the load
balanced frontends running Dovecot and Postfix, and the third machine is
our NFS.  Over the past 4 months or so, I've tweaked and optimized our mail
servers, and we receive roughly 3 million emails a day combined through
this setup.  

Sometimes, the IO Wait is horrible on the load balanced servers - it can
get up into the 80-90% range sometimes - it's usually when a lot of email
is being passed, or there are a lot of POP3 and IMAP connections.

One item which I believe to be hurting I/O performance is the fact I used a
RAID 10 setup using SATA II drives on an LSI Logic SATA I controller, in 32
bit mode.  Until we rebuild our mail setup (which may be another year down
the road), I want to make sure these servers are optimized to the fullest
just in case we get heavy I/O usage, it doesn't slow down if at all
possible.

One thing I noticed is that when issuing a 'ps aux | grep -i pop' or 'ps
aux | grep -i imap' I see the same username 2,3,4,5 times, sometimes more. 
When issuing a 'tail -f /var/log/dovecot.log' I notice that some users log
into POP3 every 3 seconds, sometimes sooner.

Without upsetting the customer, is there anything I can do on my end to
disallow people logging into POP3 multiple times at once?  

Any tips on this is very much appreciated.  Thanks in advance.

Patrick