SPF Record with Multiple Servers

Hi all,

I've a question about the SPF setup in my domain.

We have two MTAs: an exchange server that does not use SMTP to relay messag=
es to the Internet and a Postfix Mail Gateway on the border to send and rec=
eive messages to/from the internet.

The clients connect on the Exchange Server to relay messages to the externa=
l world. So an SMTP connection would start in the Exchange, then it relays =
to the Postfix server and then to the Internet. On the other hand when a me=
ssage come from the Internet it first arrives in the Postfix server and aft=
er the processing it's handled to the Exchange server.

The question is: which SPF TXT string I should use?

The Postfix server is my only MX. And I don't know if I should include the =
Exchange Server name in the SPF rules.

I was considering: vspf=3D1 mx -all

But this does not include the Exchange, and I don't know if it's right or n=
ot.

Thanks in advance,

Sent from my iPhone=