Override MX for a domain?

If I set the MX record of a domain I host in MIAB will that have MIAB route all mail for that domain to the other mail server I have setup?

The reason for this is because it uses LDAP authentication and I would like to use that for a corporate email I host for a company. they would like LDAP auth and I would rather not have to setup in my registrars DNS settings as that takes time to do.

So my question is exactly this:

In the Custom DNS page I can set an MX record, will this override the default MX record set for a domain I host in MIAB? Will this also override DKIM/SPF records as well? or will those need to be set separately?

If you have a MX record in DNS, any incoming email will be routed to the MX Record with the lowest Preference value.

Yes this overrides MIAB’s current MX for the selected host.

In Admin panel -> System -> Custom DNS:

Type: MX
Text: 20 mail.example.com