Postini and SMTP mail servers

[#1]

Will it be possible to use postini through PlusNet if you host your own smtp mail server such as Microsoft exchange?

[#2]

No, unfortunately our systems do not allow this.

[#3]

The reason is the SMTP setting means all mail will be delivered by the sending mail server direct to your IP address, bypassing PlusNet completely so they can't add postini to the connection as they have no involvement in the email delivery process.

[#4]

How come Google can offer this service for smtp mail if Plusnet cant?
http://www.google.com/a/help/intl/en/security/compare.html

[#5]

Because mail is not sent direct to you but via Google who then sends it to you. PlusNet's mail implementation is not  designed to work that way.