We want to place a spf record in our external DNS zone, but wanna make sure
we don't screw up our own email in the process.

The SMTP protocol that the Sender ID filter is attached to uses external
DNSs.  Would the Sender ID Filter then use the external DNSs or the ones
configured on the OS?

What effect can the spf record have on POP users.  When they send an email,
the first IP is the PC they are on.  Will there be issue if the IP listed in
the spf record is the second one listed in the email header?

Has anyone out in a spf record on their AD DNS zone in order to stop being
spoofed with your own domain name?

Does anyone know of a good Sender ID community for Exchange 2003 that I might
find an answer from?

Exchange 2003 and Active Directory Users and Computers.
Multiple people using 1 mailbox HELP !!
OAL (apparently) 0x8004010F
Email rejection
Mysterius emails