Setting up SMTP Relay

**countach44** · 03-28-2008, 09:54 PM

I have an isolated network from which I would like to be able to send mail out of to host mydomain.com. I have configured an SMTP (postfix) server with external access to relay the mail. I have tested this via telnet and it works fine. Now I am trying to configure sendmail on the clients to use my server as a relay. I have tried a number of options, but haven't had much success. Here's what I've done (I've also done the makes for m4 configs and makemaps for the hashes, but have omitted the commands for brevity):

The SMTP server has the hostname 'myrelay' in all the configurations below...

In sendmail.mc:
created this line:

Code:

define(`SMART_HOST', `myrelay')dnl

and ran the make

Then I tried this:
In mailertable:

Code:

mydomain.com    smtp:[myrelay]

I included the brackets because there is no MX record for 'myrelay'

Any thoughts on what I could be missing?

Note: I prefer to use postfix, as I am far more familiar with the configuration, but in this situation I am required to use sendmail for the clients.

**countach44** · 04-03-2008, 03:59 AM

Well, apparently the issue was that the machine trying to relay the message couldn't resolve mydomain.com in DNS. Adding a bogus IP in /etc/hosts for mydomain.com works. Strange, eh? Anyone know if there's a way to tell sendmail to leave DNS resolution for the smart host? Seems kinda bad not to, adding something to /etc/hosts is a patchwork solution that I'm not a fan of...

**Kernel_Killer** · 04-06-2008, 06:29 PM

Do you have mydomain.com setup in /etc/resolv.conf (i.e. 1st line 'search mydomain.com'), and is your domain name of the system set the same?

**countach44** · 04-07-2008, 12:22 AM

No - intentionally. This server is in it's own network, which doesn't have access to external machines (part of mydomain.com).
There are some servers, however, like 'myrelay' which does have a second interface and has access to both networks.
The server I am trying to configure should ideally relay all mail through 'myrelay,' except for mail destined for the local machine. I was hoping this could be done without trying to resolve the destination address since the relay should worry about that...