How to add MX record for subdomain?

I need help setting up MX record for my subdomain. I have two vps, on vps1 I host the website and vps2 use it for emailing.

I was able to successful setup all the domains by doing this. Added mx A record pointing to the vps2 ip (1.12.1.123) and the added MX record.

Code: [Select]

domain.com.      0      IN      MX      5      mx.domain.com.
mx      0      IN      A      1.12.1.123
I'm not sure if that's the best way to do it but it works. The only thing now is that subdomain emails are not working. How do I set that up?