[CentOS] Dovecot attack

Mon Aug 23 09:58:56 UTC 2010
Timothy Murphy <gayleard at eircom.net>

It seems there was some kind of attack against dovecot on my server
(CentOS-5.5) with a hundred or so logwatch entries like:
=========================================
**Unmatched Entries**
dovecot-auth: pam_succeed_if(dovecot:auth): 
  error retrieving information about user admin
dovecot-auth: pam_succeed_if(dovecot:auth): 
  error retrieving information about user webmaster
=========================================

I googled for this, and it seems quite a common occurrence.

Basically, I'm wondering whether this is best met
at the dovecot level, or at my firewall?
I'm running shorewall, and I see advice 
to impose a time-interval between successive attempts like these,
but I'm not sure of the best way to do this?

-- 
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland