Limiting number of mail(imap/pop) connections per user per IP

[Naresh V]

Hi,

In real IMAP servers like Dovecot, there is a way to limit the number
of connections made by a username from a particular IP.
Now that nginx is going to sit in front of my dovecot - I won't be
able make use of this limit in dovecot anymore (dovecot will see only
my nginxes IPs as client IP)

How can I achieve this sort of limiting at the nginx level itself?

-Naresh V.