User Guide

CHAPTER
4-1
AsyncOS 9.1.2 for Cisco Email Security Appliances User Guide
4
Understanding the Email Pipeline
• Overview of the Email Pipeline, page 4-1
• Email Pipeline Flows, page 4-1
• Incoming / Receiving, page 4-4
• Work Queue / Routing, page 4-7
• Delivery, page 4-10
Overview of the Email Pipeline
The Email Pipeline is the flow of email as it is processed by the appliance. It has three phases:
• Receipt — As the appliance connects to a remote host to receive incoming email, it adheres to
configured limits and other receipt policies. For example, verifying that the host can send your users
mail, enforcing incoming connection and message limits, and validating the message’s recipient.
• Work Queue — The appliance processes incoming and outgoing mail, performing tasks such as
filtering, safelist/blocklist scanning, anti-spam and anti-virus scanning, Outbreak Filters, and
quarantining.
• Delivery — As the appliance connects to send outgoing email, it adheres to configured delivery
limits and policies. For example, enforcing outbound connection limits and processing
undeliverable messages as specified.
Email Pipeline Flows
Figure 4-1, Figure 4-1, and Figure 4-3 provide an overview of how email is processed through the
system, from reception to routing to delivery. Each feature is processed in order (from top to bottom).
You can test most of the configurations of features in this pipeline using the
trace command.