Mail servers make heavy use of DNS resolution. The Mail exchanger (commonly referred to as MX) field in the DNS records should be updated and verified so that incoming mail can be directed to the new mail server.
A discussion on DNS records is beyond the scope of this tutorial. However, a sample record is shown as an example.
$TTL 86400 ; Default TTL example.com. IN SOA ns0.example.com. admin.example.org. ( 2005031401 ; serial 10800 ; Refresh period 3600 ; Retry interval 604800 ; Expire time 10800 ; Negative caching TTL )
$ORIGIN example.com. IN NS ns0.example.com. IN NS ns1.example.com. IN MX 1 example.com. IN A 10.4.160.3
www IN CNAME example.com. mail IN CNAME example.com.
