Sender Verification and Callouts differences

[teddymills]

Sender Verification Callouts

Use callouts to verify the existence of email senders.
Exim will connect to the mail exchanger for a given address to verify it exists before accepting mail from it.


Sender Verification
Verify that the domain mail reports as it origin actually exists

Can someone word this second one differently.
What is it exactly doing?

[anushkumar]

To be simple : It checks whether the email sender exists on the origin server or not.