Deny MX queries for dynamic IP pools

[Kevin Darcy]

On 1/31/2010 4:18 PM, SM wrote:
> At 05:25 31-01-10, Wael Shaheen wrote:
>> As a solution the routing team was thinking to block port 25 for 
>> outgoing as
>> some ISPs do. However, I do not see this to be a valid solution for many
>> reasons such as clients that have email servers outside, or if 
>> decided to be
>> redirected to spam filters then that will just cost the company too 
>> much.
>
> Mail submission is done over port 587 and not port 25.
MTA-to-MTA traffic uses port 25.

Also, older MUAs will still often use port 25 even for message 
submission, and so will spammers, if they think it will help them bypass 
anti-spam protections built into the MSA.

                                                                         
                                                                         
- Kevin