That is what happens by default basically. Except …
Your terminology is incorrect here … I am presuming you mean “and point the IP address of the VPS I will be using for Mail-in-a-Box” to those two glue records.
If that is not correct, then you are doing something wrong.
Please refer to my response to your other post on this topic: MIAB - domain name vs subdomain - security concern? - #5 by alento