My host provides an smtp server for sending mail. I want to setup sendmail to relay all emails to the hosts smtp server. How do you do that?
It's a little difficult to answer your question without more context on your email environment. That being said, the general steps would be:
1) Edit /etc/mail/sendmail.cf
2) Search for "DS"
You'll find a section that looks like this:
# "Smart" relay host (may be null) DSrelay:
3) Put the downstream mail server IP in the square brackets.
4) Save changes. Bounce sendmail service.
Again, I have to reiterate that this is a general guideline. Your mileage may vary.