User Guide for AsyncOS 9.6 for Cisco Email Security Appliances

1207 Pages·2015·11.27 MB·English

by  Cisco Systems

User Guide for AsyncOS 9.6 for Cisco
Email Security Appliances
Published: July 6, 2015
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User Guide for AsyncOS 9.6 for Cisco Email Security Appliances
© 2015 Cisco Systems, Inc. All rights reserved.
C O N T E N T S
CHAPTER 1 Getting Started with the Cisco Email Security Appliance 1-1
What’s New in This Release 1-1
What’s New in AsyncOS 9.6 for Cisco Email Security Appliances 1-1
What’s New in AsyncOS 9.5 for Cisco Email Security Appliances 1-2
Changed Behavior 1-4
Changed Behavior in AsyncOS 9.6 for Cisco Email Security Appliances 1-4
Changed Behavior in AsyncOS 9.5 for Cisco Email Security Appliances 1-4
Where to Find More Information 1-4
Documentation 1-5
Training 1-5
Cisco Notification Service 1-6
Knowledge Base 1-6
Cisco Support Community 1-6
Cisco Customer Support 1-6
Third Party Contributors 1-7
Cisco Welcomes Your Comments 1-7
Registering for a Cisco Account 1-7
Cisco Email Security Appliance Overview 1-7
Supported Languages 1-8
CHAPTER 2 Accessing the Appliance 2-1
Web-based Graphical User Interface (GUI) 2-1
Browser Requirements 2-1
Accessing the GUI 2-1
Changing Configuration Settings 2-2
Configuration Changes 2-2
Commit or Abandoning Changes 2-3
Command Line Interface (CLI) 2-3
CHAPTER 3 Setup and Installation 3-1
Installation Planning 3-1
Review Information That Impacts Planning Decisions 3-1
Plan to Place the Email Security Appliance at the Perimeter of Your Network 3-1
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Register the Email Security Appliance in DNS 3-2
Installation Scenarios 3-3
Physically Connecting the Email Security Appliance to the Network 3-5
Configuration Scenarios 3-5
Preparing for System Setup 3-8
Determine Method for Connecting to the Appliance 3-8
Determining Network and IP Address Assignments 3-9
Gathering the Setup Information 3-11
Using the System Setup Wizard 3-13
Accessing the Web-Based Graphical User Interface (GUI) 3-14
Defining Basic Configuration Using the Web-Based System Setup Wizard 3-14
Setting up the Connection to Active Directory 3-22
Proceeding to the Next Steps 3-22
Accessing the Command Line Interface (CLI) 3-23
Running the Command Line Interface (CLI) System Setup Wizard 3-23
Configuring your system as an Enterprise Gateway 3-37
Verifying Your Configuration and Next Steps 3-37
CHAPTER 4 Understanding the Email Pipeline 4-1
Overview of the Email Pipeline 4-1
Email Pipeline Flows 4-1
Incoming / Receiving 4-4
Host Access Table (HAT), Sender Groups, and Mail Flow Policies 4-5
Received: Header 4-5
Default Domain 4-5
Bounce Verification 4-5
Domain Map 4-6
Recipient Access Table (RAT) 4-6
Alias Tables 4-6
LDAP Recipient Acceptance 4-6
SMTP Call-Ahead Recipient Validation 4-6
Work Queue / Routing 4-7
Email Pipeline and Security Services 4-7
LDAP Recipient Acceptance 4-7
Masquerading or LDAP Masquerading 4-8
LDAP Routing 4-8
Message Filters 4-8
Email Security Manager (Per-Recipient Scanning) 4-8
Quarantines 4-10
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Delivery 4-10
Virtual gateways 4-11
Delivery Limits 4-11
Domain-Based Limits 4-11
Domain-Based Routing 4-11
Global Unsubscribe 4-11
Bounce Limits 4-12
CHAPTER 5 Configuring the Gateway to Receive Email 5-1
Overview of Configuring the Gateway to Receive Email 5-1
Working with Listeners 5-2
Configuring Global Settings for Listeners 5-6
Settings for Messages Containing Multiple Encodings 5-8
Listening for Connection Requests by Creating a Listener Using Web Interface 5-8
Partial Domains, Default Domains, and Malformed MAIL FROMs 5-12
Listening for Connection Requests by Creating a Listener Using CLI 5-13
Advanced HAT Parameters 5-14
Enterprise Gateway Configuration 5-15
CHAPTER 6 Sender Reputation Filtering 6-1
Overview of Sender Reputation Filtering 6-1
SenderBase Reputation Service 6-1
SenderBase Reputation Score (SBRS) 6-2
How SenderBase Reputation Filters Work 6-3
Recommended Settings for Different Sender Reputation Filtering Approaches 6-4
Editing Sender Reputation Filtering Score Thresholds for a Listener 6-5
Testing Sender Reputation Filtering Using the SBRS 6-6
Monitoring the Status of the SenderBase Reputation Services 6-7
Entering Low SBRS Scores in the Message Subject 6-7
CHAPTER 7 Defining Which Hosts Are Allowed to Connect Using the Host Access Table (HAT) 7-1
Overview of Defining Which Hosts Are Allowed to Connect 7-1
Default HAT Entries 7-2
Defining Remote Hosts into Sender Groups 7-3
Sender Group Syntax 7-4
Sender Groups Defined by Network Owners, Domains, and IP Addresses 7-4
Defining Sender Groups by SenderBase Reputation Score 7-6
Sender Groups Defined by Querying DNS Lists 7-7
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Defining Access Rules for Email Senders Using Mail Flow Policies 7-8
HAT Variable Syntax 7-9
Understanding Predefined Sender Groups and Mail Flow Policies 7-11
Handling Messages from a Group of Senders in the Same Manner 7-13
Creating a Sender Group for Message Handling 7-13
Adding a Sender to an Existing Sender Group 7-14
Rearranging the Order of the Rules to Perform for Incoming Connections 7-14
Searching for Senders 7-15
Defining Rules for Incoming Messages Using a Mail Flow Policy 7-15
Defining Default Values for Mail Flow Policies 7-20
Working with the Host Access Table Configuration 7-21
Exporting the Host Access Table Configuration to an External File 7-21
Importing the Host Access Table Configuration from an External File 7-21
Using a List of Sender Addresses for Incoming Connection Rules 7-22
SenderBase Settings and Mail Flow Policies 7-23
Timeouts for SenderBase Queries 7-23
HAT Significant Bits Feature 7-24
Verifying Senders 7-25
Sender Verification: Host 7-26
Sender Verification: Envelope Sender 7-26
Implementing Sender Verification — Example Settings 7-28
Testing Your Settings for Messages from Unverified Senders 7-33
Sender Verification and Logging 7-35
7-35
CHAPTER 8 Accepting or Rejecting Connections Based on Domain Name or Recipient Address 8-1
Overview of Accepting or Rejecting Connections Based on the Recipient’s Address 8-1
Overview of the Recipient Access Table (RAT) 8-2
Accessing the RAT 8-2
Editing the Default RAT Entry 8-2
Domains and Users 8-3
Adding Domains and Users For Which to Accept Messages 8-3
Rearranging the Order of Domains and Users in the Recipient Access Table 8-5
Exporting the Recipient Access Table to an External File 8-5
Importing the Recipient Access Table from an External File 8-6
CHAPTER 9 Using Message Filters to Enforce Email Policies 9-1
Overview 9-1
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Components of a Message Filter 9-2
Message Filter Rules 9-2
Message Filter Actions 9-2
Message Filter Example Syntax 9-3
Message Filter Processing 9-4
Message Filter Order 9-4
Message Header Rules and Evaluation 9-5
Message Bodies vs. Message Attachments 9-5
Thresholds for Matches in Content Scanning 9-6
AND Test and OR Tests in Message Filters 9-9
Message Filter Rules 9-10
Filter Rules Summary Table 9-10
Regular Expressions in Rules 9-17
Smart Identifiers 9-21
Description and Examples of Message Filter Rules 9-22
Message Filter Actions 9-49
Filter Actions Summary Table 9-49
Action Variables 9-56
Matched Content Visibility 9-58
Description and Examples of Message Filter Actions 9-58
Attachment Scanning 9-78
Message Filters for Scanning Attachments 9-79
Image Analysis 9-80
Configuring the Image Analysis Scanning Engine 9-80
Configuring the Message Filter to Perform Actions Based on Image Analysis Results 9-83
Notifications 9-85
Examples of Attachment Scanning Message Filters 9-85
Using the CLI to Manage Message Filters 9-89
Creating a New Message Filter 9-90
Deleting a Message Filter 9-91
Moving a Message Filter 9-91
Activating and Deactivating a Message Filter 9-91
Importing Message Filters 9-95
Exporting Message Filters 9-95
Viewing Non-ASCII Character Sets 9-95
Displaying a Message Filter List 9-96
Displaying Message Filter Details 9-96
Configuring Filter Log Subscriptions 9-96
Changing Message Encoding 9-98
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Sample Message Filters 9-100
Message Filter Examples 9-106
Open-Relay Prevention Filter 9-106
Policy Enforcement Filters 9-107
Routing and Domain Spoofing 9-111
Configuring Scan Behavior 9-114
CHAPTER 10 Mail Policies 10-1
Overview of Mail Policies 10-1
How to Enforce Mail Policies on a Per-User Basis 10-2
Handling Incoming and Outgoing Messages Differently 10-3
Matching Users to a Mail Policy 10-4
First Match Wins 10-4
Examples of Policy Matching 10-4
Message Splintering 10-6
Managed Exceptions 10-7
Configuring Mail Policies 10-7
Configuring the Default Mail Policy for Incoming or Outgoing Messages 10-7
Creating a Mail Policy for a Group of Senders and Recipients 10-8
Finding Which Policies Apply to a Sender or Recipient 10-11
CHAPTER 11 Content Filters 11-1
Overview of Content Filters 11-1
How Content Filters Work 11-1
How to Scan Message Content Using a Content Filter 11-2
Content Filter Conditions 11-2
Content Filter Actions 11-9
Action Variables 11-14
Filtering Messages Based on Content 11-16
Creating a Content Filter 11-16
Enabling Content Filters for All Recipients by Default 11-17
Applying the Content Filter to Messages for a Certain User Group 11-18
Notes on Configuring Content Filters in the GUI 11-18
CHAPTER 12 Anti-Virus 12-1
Anti-Virus Scanning Overview 12-1
Evaluation Key 12-2
Scanning Messages with Multiple Anti-Virus Scanning Engines 12-2
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Sophos Anti-Virus Filtering 12-2
Virus Detection Engine 12-3
Virus Scanning 12-3
Detection Methods 12-3
Virus Descriptions 12-4
Sophos Alerts 12-4
When a Virus is Found 12-4
McAfee Anti-Virus Filtering 12-5
Pattern-Matching Virus Signatures 12-5
Encrypted Polymorphic Virus Detection 12-5
Heuristics Analysis 12-5
When a Virus is Found 12-6
How to Configure the Appliance to Scan for Viruses 12-6
Enabling Virus Scanning and Configuring Global Settings 12-7
Configuring Virus Scanning Actions for Users 12-7
Configuring the Anti-Virus Policies for Different Groups of Senders and Recipients 12-13
Notes on Anti-Virus Configurations 12-14
Flow Diagram for Anti-Virus Actions 12-15
Sending an Email to the Appliance to Test Anti-Virus Scanning 12-16
Updating Virus Definitions 12-18
About Retrieving Anti-Virus Updates via HTTP 12-18
Configuring Update Server Settings 12-18
Monitoring and Manually Checking for Anti-Virus Updates 12-18
Verifying Anti-Virus Files Have Updated on the Appliance 12-19
CHAPTER 13 Anti-Spam 13-1
Overview of Anti-Spam Scanning 13-1
Anti-Spam Solutions 13-2
How to Configure the Appliance to Scan Messages for Spam 13-2
IronPort Anti-Spam Filtering 13-3
Evaluation Key 13-3
Cisco Anti-Spam: an Overview 13-4
Configuring IronPort Anti-Spam Scanning 13-5
Cisco Intelligent Multi-Scan Filtering 13-6
Configuring Cisco Intelligent Multi-Scan 13-7
Defining Anti-Spam Policies 13-7
Understanding Positive and Suspect Spam Thresholds 13-10
Configuration Examples: Actions for Positively Identified versus Suspected Spam 13-11
Unwanted Marketing Messages From Legitimate Sources 13-11
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Using Custom Headers to Redirect URLs in Suspected Spam to the Cisco Web Security Proxy:
Configuration Example 13-11
Enabling Different Anti-Spam Scanning Engines in Different Mail Policies: Configuration
Example 13-12
Protecting Appliance-Generated Messages From the Spam Filter 13-14
Headers Added During Anti-Spam Scanning 13-14
Reporting Incorrectly Classified Messages to Cisco Systems 13-15
Determining Sender IP Address In Deployments with Incoming Relays 13-15
Example Environments with Incoming Relays 13-15
Configuring the Appliance to Work with Incoming Relays 13-17
How Incoming Relays Affect Functionality 13-21
Configuring Logs to Specify Which Headers Are Used 13-23
Monitoring Rules Updates 13-23
Testing Anti-Spam 13-24
Sending an Email to the Appliance to Test Cisco Anti-Spam 13-25
Ways Not to Test Anti-Spam Efficacy 13-26
CHAPTER 14 Managing Graymail 14-1
Overview of Graymail 14-1
Graymail Management Solution in Email Security Appliance 14-1
Graymail Classification 14-2
How Graymail Management Solution Works 14-3
How Safe Unsubscribing Works 14-4
Configuring Graymail Detection and Safe Unsubscribing 14-5
Requirements for Graymail Detection and Safe Unsubscribing 14-6
Graymail Detection and Safe Unsubscribing in Cluster Configurations 14-6
Enable Graymail Detection and Safe Unsubscribing 14-6
Configuring the Incoming Mail Policy for Graymail Detection and Safe Unsubscribing 14-6
Bypassing Graymail Actions using Message Filters 14-8
Monitoring Graymail 14-8
Updating Graymail Rules 14-9
Customizing the Appearance of Unsubscribe Page for End Users 14-9
End-User Safelist 14-10
Viewing Logs 14-10
CHAPTER 15 Outbreak Filters 15-1
Overview of Outbreak Filters 15-1
How Outbreak Filters Work 15-2
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