Understanding sender_access

[Alex Regan]

Hi,

I'm trying to understand how to reject mail not within my domain 
claiming it's from my domain. I understand body_checks can be used to 
block mail "From:" my domain, and check_sender_access can be used to 
block "MAIL FROM" my domain, but don't understand the implications of 
doing that.

I have postfix set up on a mail relay which accepts mail from the 
Internet and forwards to an internal Exchange server. This Exchange 
server is the only server responsible for outbound mail.

There are no mobile users, but on occasion mail is sent from bulk 
mailers as being "From:" our domain. I'm concerned that by implementing 
body_checks or a sender map could reject these emails. Do these bulk 
mailers generally have a common setup where they can be configured to 
use smtp-auth for this?

I'm hoping someone can provide some general guidance on how to configure 
my system to permit trusted senders to use our domain while spammers 
trying to use "From:" our domain are rejected.

Is this type of spoofing generally a concern? Is typically SPF the best 
approach?

Thanks,
Alex