[CentOS] SPAM on the List

[Ljubomir Ljubojevic]

Devin Reade wrote:
> Ljubomir Ljubojevic <office at plnet.rs> wrote:
> 
>> I use it too. Reverse-DNS check is best SPAM repellent there is. Only 
>> mail from properly set mail servers is accepted.
> 
> That's fine if your check is that a reverse DNS entry exists,
> or that the HELO/ELHO exists in forward DNS or, if your MTA is
> smart enough, it does a reverse-forward* check, but if
> you only check that the HELO/ELHO matches the reverse entry
> then you're blocking a bunch of valid mailers because there is
> no specification requirement that those two match (and they don't
> in the general case).
> 
> (*) reverse-forward here means do a reverse lookup on the connecting
> IP, then doing a forward lookup on the result, and then ensure that
> original IP is one of the 'A' records resolved from the forward 
> lookup.
> 
> Devin

I only check reverse DNS entry for FQDN, I think HELO/EHLO is not checked.

Ljubomir