The WordPress support site says "Please note that you cannot add an A record for a root level domain such as mydomain.com through the WordPress.com Custom DNS editor." The URL for this quote is http://en.support.wordpress.com/domain-mapping/custom-dns/
However, I'm wondering if I could use the WordPress.com Custom DNS editor to add an A record for a SUBDOMAIN such as mail.example.com.
If so, what EXACT line of code would accomplish this? I need to make an A record for mail.example.com which points to a specific IP address. The reason I want to do this is I want to then have an MX record point to the A record.