Hello,

   If I understood the problem correctly you must use the following

   iptables -A FORWARD -s x.x.x.a -p tcp --dport 25 -j ACCEPT
   iptables -A FORWARD -s x.x.x.b -p tcp --dport 25 -j ACCEPT

   iptables -A FORWARD -s x.x.x.0/24 -p tcp --dport 25 -j  REJECT

   Or if you have more than two host you want to gran SMTP access put 
the following into a script:
    ...
    #Here you could add as much as you need IP addresses or hostnames 
separated by space
    allowed_smpt="x.x.x.a   x.x.x.b   x.x.x.c   x.x.x.d"
        for allowed in $allowed_smpt
    do
       iptables -A FORWARD -s $allowed -p tcp --dport 25 -j ACCEPT
    done

    iptables -A FORWARD -s x.x.x.0/24 -p tcp --dport 25 -j REJECT
    ...

Hope this will help
Regards :)

Heupink, Mourik Jan C. wrote:

>Hello all.
>
>The subject says it all, really. I want to (of course) allow OUTGOING mail
>from our domain, from only two designated servers. So, drop outgoing mail
>from any other host.
>
>I can't seem to produce the iptables command to get this to work... (using
>forward chain, because using transp. bridging firewall...)
>
>I guess this: iptables -A FORWARD -s x.x.x.0/24 -p tcp --dport 25 -REJECT
>would drop all outgoing mail, right? (i guess the way to select outgoing
>mail traffic would be to use --dport..?)
>
>Now i have to find a way to make an exclusion in that rule. something like
>-s x.x.x.0/24 EXCEPT x.x.x.y
>
>Could anyone shed some light onto this..?
>
>Thanks very much in advance,
>Yours,
>Mourik Jan
>
>
>
>
>  
>