Nigel,
In my first email on the topic, I noted:
"- Your mail server must be configured with the hostname name noted in the A Record"
For example if the domain you are establishing email for is foo.com and your server is mail.example.com, and the IP of this server is 44.128.0.1
You must have:
- MX Record in FOO.COM pointing to MAIL.EXAMPLE.COM - an A record in EXAMPLE.COM for the host MAIL with an IP of 44.128.0.1 - 1.0.128.44.in-addr.arpa PTR's record should be MAIL.EXAMPLE.COM
Likewise, I agree that a mail server can handle mail for multiple domains, I noted to make sure that:
"- you have configured the SMTP server to receive email for the domain in which you created a global MX record entry"
-KB3VWG