IronPort - Configuration Guide - AsyncOS 7.6.1

4-2
Cisco IronPort AsyncOS 7.6 for Email Configuration Guide
Chapter 4 Understanding the Email Pipeline
Shaded areas in Table 4-2 represent processing that occurs in the Work Queue (see Work Queue /
Routing, page 4-6). You can test most of the configurations of features in this pipeline using the trace
command. For more information, seeDebugging Mail Flow Using Test Messages: Trace, page -446.
Table 4-1 Email Pipeline for the Cisco IronPort Appliance: Receiving Email Features
Feature Description
Host Access Table (HAT)
Host DNS Sender Verification
Sender Groups
Envelope Sender Verification
Sender Verification Exception Table
Mail Flow Policies
ACCEPT, REJECT, RELAY, or TCPREFUSE connections
Maximum outbound connections
Maximum concurrent inbound connections per IP address
Maximum message size and messages per connection
Maximum recipients per message and per hour
TCP listen queue size
TLS: no/preferred/required
SMTP AUTH: no/preferred/required
Drop email with malformed FROM headers
Always accept or reject mail from entries in the Sender
Verification Exception Table.
Received Header
SenderBase on/off (IP profiling/flow control)
Adds a received header to accepted email: on/off.
Default Domain Adds default domain for “bare” user addresses.
Bounce Verification Used to verify incoming bounce messages as legitimate.
Domain Map Rewrites the Envelope Recipient for each recipient in a
message that matches a domain in the domain map table.
Recipient Access Table (RAT) (Public listeners only) ACCEPT or REJECT recipients in RCPT
TO plus Custom SMTP Response. Allow special recipients to
bypass throttling.
Alias tables Rewrites the Envelope Recipient. (Configured system-wide.
aliasconfig is not a subcommand of listenerconfig.)
LDAP Recipient Acceptance LDAP validation for recipient acceptance occurs within the
SMTP conversation. If the recipient is not found in the LDAP
directory, the message is dropped or bounced. LDAP validation
can be configured to occur within the work queue instead.
SMTP Call-Ahead Validation SMTP call-ahead recipient validation occurs within the SMTP
conversation. The SMTP conversation is paused while the
Email Security appliance calls ahead to the external SMTP
server. The message is dropped or bounced, or the mailing
action is allowed depending on the SMTP server response.
OL-25136-01