It is not clear to me if the mail server that initiates email being sent needs to be in the SPF record or every server the mail relays through in our domain or only the last server that is directly connected to the Internet.
If our mail starts from our Exchange server and is relayed to a spam appliance and relayed again to a Unix mail server and finally out to the Internet, do we only put the last part of the chain in the SPF record (the Unix mail server) or do we also need the originating mail server (Exchange) and any other servers it relays through included in the SPF record?