Sendmail config for inbound mail and redirecting them internally to ot

[SecOS]

Hi,

I have configured a sendmail MTA for incoming mails in a network and by using IPtables i have redirected the traffic internally to other port where one more SMTP by a application is running.

Iptables rule:

iptables -A INPUT -i eth0 -p tcp --dport 25 -j ACCEPT

iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 25 -j REDIRECT --to-port 25000

My sendmail config is as below.

Sendmail.mc

define(`SMART_HOST', `relay:host.subdomain.mydomain.com')dnl

dnl # define(`RELAY_MAILER',`esmtp')dnl
define(`RELAY_MAILER_ARGS', `TCP $h 25000')dnl
define(`ESMTP_MAILER_ARGS', `TCP $h 25000')dnl
dnl #
dnl # The following causes sendmail to only listen on the IPv4 loopback address
dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl #
DAEMON_OPTIONS(`Port=smtp,Addr= "my IP address", Name=MTA-public')dnl
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA-local')dnl

/etc/services file details

smtp 25/tcp mail
smtp 25/udp mail
submission 25000/tcp # submission
submission 25000/udp # submission



after sendmail config is done i am able to receive mails , but when i applied the iptables rule as above then the mails get reject and logs will give me an error as

dsn=5.0.0, stat= deffered service unavailable

and the bounce message shows

#5.0.0 SMTP; 554 Transaction failed> #SMTP#

I am not sure what i am missing here and what to do more to fix this.

 

[SecOS]

one small thing is in the below command i missed "s" in ports.

iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 25 -j REDIRECT --to-ports 25000

Then the above steps are all corect and tested and working fine.

The issue what i faced is after setting everything the application SMTP had few issue, once they are fixed everything got fixed.