In my network I only have one machine that is configured to send email outside the network. How do I instruct my local copy of sendmail to use that server as a relay ?

http://www.google.com/search?client=...utf-8&oe=utf-8

"DS" in sendmail.cf.

0 members found this post helpful.

To tell your hosts to relay to the relay host (replace "<relayhost>" below wit the actual name of your relay host):

Uncomment the SMART HOST line (that is to say remove "dnl" from start of line) in sendmail.mc then add your relay host so it reads:
define(`SMART_HOST', `<relayhost>')dnl

After that run "make -C /etc/mail" This will add "DS<relayhost>" to sendmail.cf.
Note: The sendmail.cf package must be installed for this work. The default sendmail package on RHEL/CentOS doesn't include the make ability.

To allow relay through your relay host atlsnml1 (done on the relay host itself)
1) edit /etc/mail/access
Add the following lines:
From:<domain> RELAY
Note: You do this for each domain name that will be sending (e.g. example.com, example.net would have two separate lines). You can also add relay by hostname if you want to lock it down that way.

2) make -C /etc/mail
This recompiles mail and updates access.db from the access ascii file.

3) Stop and restart sendmail
Restarts sendmail to make the changes take effect

Note: Older sendmail installations used now deprecated untagged eentry instead:
<domain> RELAY

I think I found it in the access list under /etc/mail/access. I just added the ip address and then RELAY. Seems to be working.