zdraveite,
 vuzmozhno li e da se dobaviat dva default gateway na edin
ruter , koito rutira dva ISP.
 Ediniiat gateway da e za poshtenskiia surver (port 25,
 orientiran kum purviia ISP), a drugiiat za vsichko ostanalo
(internet , FTP,..., kum vtoriia ISP)

popregledai iproute2 spored men s nego she uspeesh :)

 imanno s nego se mucha www.lartc.org/howto , ama ne moga da
nakaram slacka da poluchava poshtata prez purviia dostavchik

 imanno s nego se mucha www.lartc.org/howto , ama ne moga da
nakaram slacka da poluchava poshtata prez purviia dostavchik

Vizh po-dobre ip rule help i ip route help
Podskazka:
ip rule "bla bla" table boza
ip route "bla bla" table boza

Uspeh

 # iptables -A PREROUTING -i eth0 -t mangle -p tcp --dport\
25  -j MARK --set-mark 1
# echo 201 mail.out >> /etc/iproute2/rt_tables
# ip rule add fwmark 1 table mail.out
 # /sbin/ip route add default via 195.96.98.253 dev ppp0
table mail.out

Dai malko obesnenie na tozi primer

 Ne si oburnal vnimanie na documentation-a, predi 2-3 godini
 v documentation-a imashe edin svesten example, i tochno toi
mi svurshi rabota po problem, koito e analogichen  s tvoia.

/sbin/ip rule add from A.B.C.D table John
/sbin/ip route add default via A.B.C.D dev ppp0 table John
/sbin/ip route flush cache
 /sbin/route add -net A.B.C.0 gw A.B.C.D netmask
255.255.255.128 ppp0

 kudeto A.B.C.D ti e IP adresa ot providera ti za mail-a,
 A.B.C.0 e net-a na providera, do koito iskash da stignesh
 prez tvoia si interface. Dobavianeto na IP/netmask na drugia
provider si stava s classic ifconfig/route commands.

 (potursi v documentation-a dumata "John", napravo sum go
copy/paste pri men :)

Poslednia red moje da stane 
 /sbin/route add -host A.B.C.1 gw A.B.C.D netmask
255.255.255.128 ppp0
 ako A.B.C.1 e gw-a ti na providera ti i ne iskash da
 komunikirash s drugi IP-ta ot negovata mreja A.B.C.0 po tozi
interface. 


A v /etc/iproute2/rt_tables imam:
#
# reserved values
#
255     local
254     main
253     default
200     John
0       unspec
#
# local
#
#1      inr.ruhep


 Vsushtnost pri men tova reshava drugi zadachi, po-obshti -
 vsichko, koeto idva na edi-koisi interface (ppp0) se vrushta
 obratno pak po nego, a ne po default gw. No na men tova mi e
 OK, shtoto drugi mashini s IP-na na tozi provider v LAN-a
 niamam, a i vruzkata kum tozi provider se polzva samo za
 mail eventualno (shtoto domain-a, koito obslujva, mai veche
 nikoi ne go znae i ne go polzva :) pri vse che si e 100%
pulna vruzka kum internet.