Cisco Cisco Email Security Appliance C160 用户指南
4-2
Cisco IronPort AsyncOS 7.6 for Email Configuration Guide
OL-25136-01
Chapter 4 Understanding the Email Pipeline
Shaded areas in
represent processing that occurs in the Work Queue (see
). You can test most of the configurations of features in this pipeline using the
trace
command. For more information, see
Debugging 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.
Verification Exception Table.
SenderBase on/off (IP profiling/flow control)
Received Header
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.
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 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.
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.