How to set up external mail server

I have an existing external mail server with the IP address and the name, and an existing website hosting account that I want to transfer to Dreamhost (just the website, not the email).

Would I (within the DH admin):

  1. set up a custom MX record to point to
  2. set up a custom A record to point mail to
  3. set up a unique IP for hosting account
  4. set the external mail server to receive mail from the unique IP
  5. transfer the DNS to DH

Does this sound right?

Steps 3 and 4 are probably not necessary. The rest looks fine.