[CentOS] Per-user limits for port access

[Sergey Podushkin]

Jussi Hirvi wrote:
> Is there a way to limit port access on a per-user basis? My practical goal
> is to limit, who is allowed to use SMTP AUTH in Sendmail. Any possible
> solutions appreciated...
> 
> Obviously, limiting by ip will not work, since the very purpose of SMTP AUTH
> is to enable mail relaying for trusted users from *anywhere*.
You could use new ability of milter-greylist (from 4.0 version), that 
provides method to limit connections by any criteria, such as remote ip, 
sender/recipient address, authentication status and many more.
You could extend configuration by using external helper, that can be 
reached by, for example, ldap or http protocols.