Hosting mail for external domains. Is this how you do it?

I’ve been using MIAB for only a very short time, and so far it is going well, with a few domains under my belt, even external websites are working.

But now I have a domain for which the client controls the DNS, and who doesn’t want to relinquish. It has entries for all kinds of services that I really wouldn’t want to screw with. They presently use Google mail, which is addressed in DNS with just a few MX records. Now we want to switch that to my MIAB setup.

I think I get how to do it, but I wanted to run it by the community. Here’s what I think needs to happen:

  1. Add an email address for the new domain as normal, as though MIAB was doing all the work.
  2. MIAB creates all DNS records for the new domain
  3. Record the MX entries that MIAB created
  4. Copy those MX records into the externally hosted DNS
  5. Ignore all DNS entries in MIAB, but remember that if the MX records change for any reason, then they need to be updated in the externally hosted domain DNS

Is this the right approach?

I have only two DNS entries added to my external site’s DNS:
MX 10 (This being the full name of my mail server)
TXT v=spf1 a mx ~all (allows mail sent from my A record host (web servere) and MX record host (MIAB server)