hello all, I am a newbie and i have the folloiwn problem with a Redhat 9.0 network i have setup:

I have a box working as the network routers. It has 2 interfaces
one for the local Lan and another to the rest fo the world.
I am running a webserver and an a mail server within the internal network. they both have 192.168.0.x numbers. I am using DNAT to forward packets destined to port 25 and 80 to accept incoming mail and http data respectively. The http part works fine, but for some reason email doesn't get to my email server. iget a response stating the router doesn't like the name of the user.
server doesn't like the username root@mydomain.com.
The dnat table: iptables -A -p tcp -d myext_int --dport 25 -j DNAT 192.168.0.x.
I don't know what is going on here...HELP

Moved: This thread is more suitable in Linux-Networking and has been moved accordingly to help your thread/question get the exposure it deserves.

I take it that you are trying to get sendmail to send external
emails through an external smtp account such as joe@bloggs.com.
Email servers will often reject emails if they are sent through
an account if the from field is something like wwrun@linux
because this doesn't match with the mailbox logon details.
You need to set up masquerading so that all external emails
are sent as though they are from joe@bloggs.com.

I have setup masquerading in sendmail.mc and used the make -C /etc/mail command to recompile it. I am sending mail from mydomain. My setup is as such:

server.mydomain.com :Router web address

mail.mydomain.com :mail server address (same ip address but mail traffice DNAT'ed to internal mailserver)

I am able to send mail from my domain, but mail sent from yahoo for example doesn't get to my mail server. Does sendmail need to be activated on the router computer as well? It seems port 25 is off when dsnedmail is turned off.

error recieved:
550 5.7.1 <hoeniola@mydomain.net>... Relaying denied