The HAT allows you to
specify hosts that are allowed to connect to a listener (that is, which hosts
you will allow to send email).
Sender Groups are
used to associate one or more senders into groups, upon which you can apply
message filters, and other Mail Flow Policies. Mail Flow Policies are a way of
expressing a group of HAT parameters (access rule, followed by rate limit
parameters and custom SMTP codes and responses).
groups and mail flow policies are defined in a listener’s HAT.
Host DNS verification
settings for sender groups allow you to classify unverified senders prior to
the SMTP conversation and include different types of unverified senders in your
various sender groups.
While the connecting
host was subject to Host DNS verification in sender groups — prior to the SMTP
conversation — the domain portion of the envelope sender is DNS verified in
mail flow policies, and the verification takes place during the SMTP
conversation. Messages with malformed envelope senders can be ignored. You can
add entries to the Sender Verification Exception Table — a list of domains and
email addresses from which to accept or reject mail despite envelope sender DNS
filtering allows you to classify email senders and restrict access to your
email infrastructure based on sender’s trustworthiness as determined by the
Cisco SenderBase Reputation Service.
For more information,
Understanding Predefined Sender Groups and Mail Flow Policies.