Sendmail config when MX record points to another server

If your domain mail is hosted on mail server in a different domain, you should tell your sendmail about it. Otherwise if you try to send a mail to a user in your local domain, you will get an error from sendmail at /vat/log/mail.log:

User unknown.

It means that sendmail is trying to find user, that is mentioned in a message, on your local server and can’t find that user, because we use mail server that is hosted on different IP-address. To solve this problem we should tell sendmail to search for mail users with our domain name on the remote server.

Open /etc/mail/ for edit:

sudo nano /etc/mail/

Add this two lines to the end of the file:

define(`MAIL_HUB', `')dnl
define(`LOCAL_RELAY', `')dnl

Press “Ctrl + X” when you are done and answer “Y” for question about saving a file.

Now we should reload sendmail service:

service sendmail reload

And try to send mail again. If you have done everything right, emails should go through remote mail server without errors.