Incoming email not receiving.

[Me.B]

1. MX should be a CNAME to another domain not to the IP.

Example:

@ MX point to mail.domain.com
Then you create an A record mail pointing to the server IP.
You need to have 2 records setup CNAME + A so MX works.

If you wand to add pop.domain.com the easy way is another cname pointing to mail.domain.com.

2. If you use external dns you don't need to create ns1 & ns2 pointing to server IP as those DNS entries won't be used.

I don't get the point over server doors? You mean ports? DNS don't care about ports as long the DNS entry resolve correctly.

Hope it helps
M B