In order to point your MX record at a specific IP address, you first need an A record for it to point to. As you have a web server, then you probably have one already:
domain.com. 14400 IN A <ip address>
So your MX record would want to look like this:
domain.com. 14400 IN MX 0 domain.com.
This says "Emails for domain.com should be delivered to the server with the IP address that domain.com resolves to".
It is often a good idea to create a separate A record for your email so you can separate email from the webserver down the track if you need to:
mail.domain.com. 14400 IN A <ip address>
domain.com. 14400 IN MX 0 mail.domain.com.