Cisco Cisco Email Security Appliance C170 Guía Del Usuario
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Cisco AsyncOS 9.1 for Email User Guide
Chapter 4 Understanding the Email Pipeline
Incoming / Receiving
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Host Access Table (HAT), Sender Groups, and Mail Flow Policies
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).
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).
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).
Together, sender 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.
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 verification settings.
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 verification settings.
Sender reputation 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.
infrastructure based on sender’s trustworthiness as determined by the Cisco SenderBase Reputation
Service.
For more information, see
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Received: Header
Using the
listenerconfig
command, you can configure a listener to not include the Received: header
by default to all messages received by the listener.
For more information, see “Advanced Configuration Options” in the “Customizing Listeners” chapter.
Default Domain
You can configure a listener to automatically append a default domain to sender addresses that do not
contain fully-qualified domain names; these are also known as “bare” addresses (such as “joe” vs.
“joe@example.com”).
contain fully-qualified domain names; these are also known as “bare” addresses (such as “joe” vs.
“joe@example.com”).
For more information, see “SMTP Address Parsing Options” in the “Customizing Listeners” chapter.
Bounce Verification
Outgoing mail is tagged with a special key, and so if that mail is sent back as a bounce, the tag is
recognized and the mail is delivered. For more information, see “Bounce Verification” in the
“Configuring Routing and Delivery Features” chapter.
recognized and the mail is delivered. For more information, see “Bounce Verification” in the
“Configuring Routing and Delivery Features” chapter.