Cisco Cloud Email Security User guide

Brand: Cisco

Model: Cloud Email Security

Category: Software

Type: User guide

This manual is also suitable for

User Guide for AsyncOS 12.5 for Cisco Cloud Email Security - GD

(General Deployment)

First Published: 2019-07-01

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CONTENTS

Getting Started with Cisco Email Security 1

CHAPTER 1

What's New in AsyncOS 12.5 1

Where to Find More Information 7

Documentation 8

Training 8

Cisco Notification Service 9

Knowledge Base 9

Cisco Support Community 9

Cisco Customer Support 9

Third Party Contributors 10

Cisco Welcomes Your Comments 10

Registering for a Cisco Account 10

Cisco Email Security Appliance Overview 10

Supported Languages 11

Accessing the Appliance 13

CHAPTER 2

Web-based Graphical User Interface (GUI) 13

Browser Requirements 13

Accessing the GUI 14

Factory Default Username and Passphrase 14

Centralized Management 14

Cloud Administrator - Web Interface Access 15

Enhanced User Experience using How-Tos Widget 15

Disabling How-Tos Widget on the Appliance 16

Changing Configuration Settings 16

Configuration Changes 16

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Commit or Abandoning Changes 16

Command Line Interface (CLI) 17

Cloud Administrator - CLI Access 17

Setup and Installation 19

CHAPTER 3

Installation Planning 19

Review Information That Impacts Planning Decisions 19

Plan to Place the Email Security Appliance at the Perimeter of Your Network 19

Installation Scenarios 21

Configuration Overview 21

Incoming 21

Outgoing 21

Ethernet Interfaces 21

Hardware Ports 22

Advanced Configurations 22

Firewall Settings (NAT, Ports) 22

Physically Connecting the Email Security Appliance to the Network 22

Configuration Scenarios 23

Segregating Incoming and Outgoing Mail 23

Preparing for System Setup 26

Determine Method for Connecting to the Appliance 27

Connecting to the Appliance 27

Determining Network and IP Address Assignments 27

Default IP Addresses for Management and Data Ports 28

Choosing Network Connections to Receive and Deliver Email 28

Binding Logical IP Addresses to Physical Ethernet Ports 28

Choosing Network Settings for Your Connections 28

Gathering the Setup Information 29

Using the System Setup Wizard 32

Accessing the Web-Based Graphical User Interface (GUI) 32

Factory Default Username and Passphrase 33

Defining Basic Configuration Using the Web-Based System Setup Wizard 33

Step 1: Start 34

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Step 2: System 34

Step 3: Network 36

Step 4: Security 40

Step 5: Review 41

Setting up the Connection to Active Directory 41

Proceeding to the Next Steps 42

Accessing the Command Line Interface (CLI) 42

Factory Default Username and Passphrase 42

Running the Command Line Interface (CLI) System Setup Wizard 43

Change the Admin Passphrase 44

Accept the License Agreement 44

Set the Hostname 44

Assign and Configure Logical IP Interface(s) 44

Specify the Default Gateway 45

Enable the Web Interface 45

Configure the DNS Settings 46

Create a Listener 46

Enable Anti-Spam 53

Select a Default Anti-Spam Scanning Engine 54

Enable the Spam Quarantine 54

Enable Anti-Virus Scanning 54

Enable Outbreak Filters and SenderBase Email Traffic Monitoring Network 54

Configure the Alert Settings and AutoSupport 55

Configure Scheduled Reporting 55

Configure Time Settings 55

Commit Changes 55

Test the Configuration 56

Immediate Alerts 56

Configuring your system as an Enterprise Gateway 56

Verifying Your Configuration and Next Steps 57

Understanding the Email Pipeline 59

CHAPTER 4

Overview of the Email Pipeline 59

Email Pipeline Flows 59

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Incoming / Receiving 62

Host Access Table (HAT), Sender Groups, and Mail Flow Policies 62

Received: Header 63

Default Domain 63

Bounce Verification 63

Domain Map 63

Recipient Access Table (RAT) 63

Alias Tables 63

LDAP Recipient Acceptance 64

SMTP Call-Ahead Recipient Validation 64

Work Queue / Routing 64

Email Pipeline and Security Services 64

LDAP Recipient Acceptance 65

Masquerading or LDAP Masquerading 65

LDAP Routing 65

Message Filters 66

Email Security Manager (Per-Recipient Scanning) 66

Safelist/Blocklist Scanning 66

Anti-Spam 66

Anti-Virus 66

Graymail Detection and Safe Unsubscribing 67

File Reputation Scanning and File Analysis 67

Content Filters 67

Outbreak Filters 67

Quarantines 67

Delivery 68

Virtual gateways 68

Delivery Limits 68

Domain-Based Limits 68

Domain-Based Routing 69

Global Unsubscribe 69

Bounce Limits 69

Configuring the Gateway to Receive Email 71

CHAPTER 5

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Overview of Configuring the Gateway to Receive Email 71

Working with Listeners 72

Configuring Global Settings for Listeners 74

Settings for Messages Containing Multiple Encodings 76

Listening for Connection Requests by Creating a Listener Using Web Interface 77

Partial Domains, Default Domains, and Malformed MAIL FROMs 81

Listening for Connection Requests by Creating a Listener Using CLI 81

Advanced HAT Parameters 82

Enterprise Gateway Configuration 84

Sender Reputation Filtering 85

CHAPTER 6

Overview of Sender Reputation Filtering 85

SenderBase Reputation Service 85

SenderBase Reputation Score (SBRS) 86

How SenderBase Reputation Filters Work 87

Recommended Settings for Different Sender Reputation Filtering Approaches 88

Editing Sender Reputation Filtering Score Thresholds for a Listener 88

Testing Sender Reputation Filtering Using the SBRS 89

Monitoring the Status of the SenderBase Reputation Services 91

Entering Low SBRS Scores in the Message Subject 91

Defining Which Hosts Are Allowed to Connect Using the Host Access Table 93

CHAPTER 7

Overview of Defining Which Hosts Are Allowed to Connect 93

Default HAT Entries 94

Defining Remote Hosts into Sender Groups 94

Sender Group Syntax 95

Sender Groups Defined by Network Owners, Domains, and IP Addresses 96

Setting Policies Based on the HAT 97

Defining Sender Groups by SenderBase Reputation Score 98

Sender Groups Defined by Querying DNS Lists 99

Defining Access Rules for Email Senders Using Mail Flow Policies 99

HAT Variable Syntax 100

Using HAT Variables 101

Testing HAT Variables 102

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Understanding Predefined Sender Groups and Mail Flow Policies 102

Handling Messages from a Group of Senders in the Same Manner 104

Creating a Sender Group for Message Handling 104

Adding a Sender to an Existing Sender Group 105

Rearranging the Order of the Rules to Perform for Incoming Connections 106

Searching for Senders 106

Defining Rules for Incoming Messages Using a Mail Flow Policy 106

Defining Default Values for Mail Flow Policies 112

Working with the Host Access Table Configuration 112

Exporting the Host Access Table Configuration to an External File 112

Importing the Host Access Table Configuration from an External File 112

Using a List of Sender Addresses for Incoming Connection Rules 113

SenderBase Settings and Mail Flow Policies 114

Timeouts for SenderBase Queries 114

HAT Significant Bits Feature 115

HAT Configuration 115

Significant Bits HAT Policy Option 115

Injection Control Periodicity 116

Verifying Senders 116

Sender Verification: Host 116

Sender Verification: Envelope Sender 117

Partial Domains, Default Domains, and Malformed MAIL FROMs 118

Custom SMTP Code and Response 118

Sender Verification Exception Table 119

Implementing Sender Verification — Example Settings 119

Throttling Messages from Unverified Senders Using the SUSPECTLIST Sender Group 120

Implementing More Stringent Throttling Settings for Unverified Senders 120

Defining Messages to Send to Unverified Senders Using the ACCEPTED Mail Flow Policy 121

Excluding Unverified Senders from Sender Verification Rules Based on Sender’s Email Address

121

Searching for Addresses within the Sender Verification Exception Table 121

Testing Your Settings for Messages from Unverified Senders 121

Sending a Test Message with a Malformed MAIL FROM Sender Address 122

Sending a Message from an Address That is Excluded from Sender Verification Rules 122

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Sender Verification and Logging 123

Envelope Sender Verification 123

Accepting or Rejecting Connections Based on Domain Name or Recipient Address 125

CHAPTER 8

Overview of Accepting or Rejecting Connections Based on the Recipient’s Address 125

Overview of the Recipient Access Table (RAT) 126

Accessing the RAT using the GUI 126

Accessing the RAT using the CLI 126

Editing the Default RAT Entry 126

Domains and Users 127

Adding Domains and Users For Which to Accept Messages 127

Defining Recipient Addresses 128

Bypassing LDAP Accept for Special Recipients 128

Bypassing Throttling for Special Recipients 129

Rearranging the Order of Domains and Users in the Recipient Access Table 129

Exporting the Recipient Access Table to an External File 129

Importing the Recipient Access Table from an External File 130

Using Message Filters to Enforce Email Policies 131

CHAPTER 9

Overview 131

Components of a Message Filter 132

Message Filter Rules 132

Message Filter Actions 132

Message Filter Example Syntax 133

Message Filter Processing 134

Message Filter Order 135

Message Header Rules and Evaluation 135

Message Bodies vs. Message Attachments 135

Thresholds for Matches in Content Scanning 136

Threshold Syntax 137

Threshold Scoring for Message Bodies and Attachments 137

Threshold Scoring Multipart/Alternative MIME Parts 137

Threshold Scoring for Content Dictionaries 138

AND Test and OR Tests in Message Filters 139

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Message Filter Rules 139

Filter Rules Summary Table 140

Regular Expressions in Rules 150

Using Regular Expressions to Filter Messages 152

Guidelines for Using Regular Expressions 152

Regular Expression and Non-ASCII Character Sets 152

n Tests 153

Case-sensitivity 153

Writing Efficient Filters 153

PDFs and Regular Expressions 154

Smart Identifiers 154

Smart Identifier Syntax 155

Description and Examples of Message Filter Rules 155

True Rule 156

Valid Rule 157

Subject Rule 157

Envelope Recipient Rule 157

Envelope Recipient in Group Rule 158

Envelope Sender Rule 158

Envelope Sender in Group Rule 159

Sender Group Rule 159

Body Size Rule 159

Remote IP Rule 160

Receiving Listener Rule 160

Receiving IP Interface Rule 161

Date Rule 161

Header Rule 161

Random Rule 162

Recipient Count Rule 163

Address Count Rule 163

Body Scanning Rule 163

Body Scanning 164

Encryption Detection Rule 164

Attachment Type Rule 165

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Attachment Filename Rule 165

DNS List Rule 166

SenderBase Reputation Rule 167

Dictionary Rules 167

SPF-Status Rule 169

SPF-Passed Rule 171

S/MIME Gateway Message Rule 171

S/MIME Gateway Verified Rule 171

Workqueue-count Rule 171

SMTP Authenticated User Match Rule 172

Signed Rule 173

Signed Certificate Rule 174

Header Repeats Rule 176

URL Reputation Rules 178

URL Category Rule 179

Corrupt Attachment Rule 179

Message Language Rule 180

Macro Detection Rule 181

Forged Email Detection Rule 181

Duplicate Boundaries Verification Rule 182

Malformed MIME Header Detection Rule 182

Geolocation Rule 183

Domain Reputation Rule for ETF 183

Domain Reputation Rule for SDR 184

Message Filter Actions 185

Filter Actions Summary Table 186

Attachment Groups 192

Action Variables 195

Non-ASCII Character Sets and Message Filter Action Variables 197

Matched Content Visibility 197

Description and Examples of Message Filter Actions 198

Skip Remaining Message Filters Action 199

Drop Action 199

Bounce Action 200

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Encrypt Action 200

S/MIME Sign or Encrypt on Delivery Action 200

S/MIME Sign or Encrypt Action 200

Notify and Notify-Copy Actions 201

Blind Carbon Copy Actions 203

Quarantine and Duplicate Actions 205

Alter Recipient Action 206

Alter Delivery Host Action 206

Alter Source Host (Virtual Gateway address) Action 207

Archive Action 207

Strip Header Action 208

Insert Header Action 208

Edit Header Text Action 209

Edit Body Text Action 209

HTML Convert Action 210

Bounce Profile Action 211

Bypass Anti-Spam System Action 211

Bypassing Graymail Actions 212

Bypass Anti-Virus System Action 212

Bypass File Reputation Filtering and File Analysis System Actions 213

Bypass Outbreak Filter Scanning Action 213

Add Message Tag Action 213

Add Log Entry Action 214

URL Reputation Actions 214

URL Category Actions 216

No Operation 217

Forged Email Detection Action 217

Attachment Scanning 217

Message Filters for Scanning Attachments 219

Image Analysis 220

Configuring the Image Analysis Scanning Engine 220

Tuning Image Analysis Settings 221

Configuring the Message Filter to Perform Actions Based on Image Analysis Results 222

Creating Content Filters to Strip Attachments Based on Image Analysis Verdicts 223

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Configuring an Action Based on Image Analysis Verdicts 223

Notifications 224

Examples of Attachment Scanning Message Filters 224

Inserting Headers 224

Dropping Attachments by File Type 225

Dropping Attachments by Dictionary Matches 226

Quarantining Protected Attachments 227

Detecting Unprotected Attachments 227

Detecting Malicious Files in Messages Attachments Using Message Filter 227

Using the CLI to Manage Message Filters 228

Creating a New Message Filter 229

Deleting a Message Filter 230

Moving a Message Filter 230

Activating and Deactivating a Message Filter 230

Activating or Deactivating a Message Filter 233

Importing Message Filters 233

Exporting Message Filters 234

Viewing Non-ASCII Character Sets 234

Displaying a Message Filter List 234

Displaying Message Filter Details 234

Configuring Filter Log Subscriptions 235

Changing Message Encoding 236

Sample Message Filters 237

Message Filter Examples 242

Open-Relay Prevention Filter 243

Policy Enforcement Filters 243

Notify Based on Subject Filter 243

BCC and Scan Mail Sent to Competitors 244

Block Specific User Filter 244

Archive and Drop Messages Filter 244

Large “To:” Header Filter 245

Blank “From:” Filter 245

SBRS Filter 245

Alter SBRS Filter 246

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Filename Regex Filter 246

Show SenderBase Reputation Score in Header Filter 246

Insert Policy into Header Filter 246

Too Many Recipients Bounce Filter 246

Routing and Domain Spoofing 247

Using Virtual Gateways Filter 247

Same Listener for Deliver and Listener Filter 247

Single Listener Filter 247

Drop Spoofed Domain Filter (Single Listener) 248

Drop Spoofed Domain Filter (Multiple Listeners) 248

Another Drop Spoofed Domain Filter 248

Detect Looping Filter 249

Configuring Scan Behavior 250

Configuring Message Handling Actions for Unscannable Messages 251

Delivering the Message 252

Sending Message to Policy Quarantine 253

Mail Policies 255

CHAPTER 10

Overview of Mail Policies 255

How to Enforce Mail Policies on a Per-User Basis 256

Handling Incoming and Outgoing Messages Differently 257

Matching Users to a Mail Policy 257

First Match Wins 258

Examples of Policy Matching 258

Example 1 259

Example 2 259

Example 3 259

Message Splintering 259

Managed Exceptions 261

Configuring Mail Policies 261

Configuring the Default Mail Policy for Incoming or Outgoing Messages 261

Creating a Mail Policy for a Group of Senders and Recipients 262

Defining Senders and Recipients for Mail Policies 262

Examples 264

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Finding Which Policies Apply to a Sender or Recipient 265

Managed Exceptions 265

Setting Priority for Message Headers 266

Content Filters 267

CHAPTER 11

Overview of Content Filters 267

How Content Filters Work 267

How to Scan Message Content Using a Content Filter 268

Content Filter Conditions 268

Content Filter Actions 276

Action Variables 283

How to Filter Messages Based on Content 284

Creating a Content Filter 285

Enabling Content Filters for All Recipients by Default 286

Applying the Content Filter to Messages for a Certain User Group 286

Notes on Configuring Content Filters in the GUI 287

Configuring Email Gateway to Consume External Threat Feeds 289

CHAPTER 12

Overview of External Threat Feeds 289

How to Configure Email Gateway to Consume External Threat Feeds 290

Obtaining External Threat Feeds Feature Key 290

Enabling External Threat Feeds Engine on Email Gateway 292

Configuring an External Threat Feed Source 292

Handling Messages Containing Threats 295

Configuring a Sender Group for Handling Messages containing Threats 296

Configuring Content or Message Filters for Handling Messages Containing Threats 296

Detecting Malicious Domains in Messages Using Content Filter 296

Creating Domain Exception List 297

Detecting Malicious Domains in Messages Using Message Filter 297

Detecting Malicious URLs in Messages Using Content Filter 298

Detecting Malicious URLs in Messages Using Message Filter 299

Detecting Malicious Files in Message Attachments Using Content Filter 301

Creating File Hash List 302

Detecting Malicious Files in Messages Attachments Using Message Filter 302

User Guide for AsyncOS 12.5 for Cisco Cloud Email Security - GD (General Deployment)

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Attaching Content Filter to Incoming Mail Policy 302

External Threat Feeds and Clusters 303

Monitoring External Threat Feeds Engine Updates 303

Viewing Alerts 303

Displaying Threat Details in Message Tracking 304

Sender Domain Reputation Filtering 305

CHAPTER 13

Overview of Sender Domain Reputation Filtering 305

SDR Verdicts 305

How to Filter Messages based on Sender Domain Reputation 307

Enabling Sender Domain Reputation Filtering on Email Gateway 308

Configuring Message or Content Filter for Handling Messages based on Sender Domain Reputation

309

Filtering Messages based on Sender Domain Reputation using Message Filter 309

Filtering Messages based on Sender Domain Reputation using Content Filter 311

Creating Domain Exception List 311

Attaching Content Filter to Incoming Mail Policy 312

Sender Domain Reputation Filtering and Clusters 312

Displaying Sender Domain Reputation Details in Message Tracking 313

Viewing Alerts 313

Viewing Logs 313

Examples of SDR Filtering Log Entries 313

Sender Domain Reputation Authentication Failure 314

Sender Domain Reputation Request Timeout 314

Sender Domain Reputation Invalid Host 314

Sender Domain Reputation General Errors 315

Anti-Virus 317

CHAPTER 14

Anti-Virus Scanning Overview 317

Evaluation Key 318

Scanning Messages with Multiple Anti-Virus Scanning Engines 318

Sophos Anti-Virus Filtering 318

Virus Detection Engine 319

Virus Scanning 319

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Detection Methods 319

Pattern Matching 319

Heuristics 320

Emulation 320

Virus Descriptions 320

Sophos Alerts 320

When a Virus is Found 320

McAfee Anti-Virus Filtering 321

Pattern-Matching Virus Signatures 321

Encrypted Polymorphic Virus Detection 321

Heuristics Analysis 321

When a Virus is Found 322

How to Configure the Appliance to Scan for Viruses 322

Enabling Virus Scanning and Configuring Global Settings 323

Configuring Virus Scanning Actions for Users 323

Message Scanning Settings 324

Message Handling Settings 324

Configuring Settings for Message Handling Actions 325

Configuring the Anti-Virus Policies for Different Groups of Senders and Recipients 328

Notes on Anti-Virus Configurations 329

Flow Diagram for Anti-Virus Actions 330

Sending an Email to the Appliance to Test Anti-Virus Scanning 331

Updating Virus Definitions 332

About Retrieving Anti-Virus Updates via HTTP 333

Configuring Update Server Settings 333

Monitoring and Manually Checking for Anti-Virus Updates 333

Manually Updating Anti-Virus Engines 333

Verifying Anti-Virus Files Have Updated on the Appliance 333

Managing Spam and Graymail 335

CHAPTER 15

Overview of Anti-Spam Scanning 335

Anti-Spam Solutions 336

How to Configure the Appliance to Scan Messages for Spam 336

IronPort Anti-Spam Filtering 337

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Evaluation Key 337

Cisco Anti-Spam: an Overview 338

Spam Scanning for International Regions 338

Configuring IronPort Anti-Spam Scanning 339

Configuring Intelligent Multi-Scan and Graymail Detection 340

Configuring Cisco Intelligent Multi-Scan 340

Managing Graymail 341

Overview of Graymail 342

Graymail Management Solution in Email Security Appliance 342

How Graymail Management Solution Works 343

Configuring Graymail Detection and Safe Unsubscribing 345

Troubleshooting Graymail Detection and Safe Unsubscribing 349

Configuring Global Settings for Intelligent Multi-Scan and Graymail Detection 350

Defining Anti-Spam Policies 350

Understanding Positive and Suspect Spam Thresholds 353

Configuration Examples: Actions for Positively Identified versus Suspected Spam 354

Unwanted Marketing Messages From Legitimate Sources 354

Using Custom Headers to Redirect URLs in Suspected Spam to the Cisco Web Security Proxy:

Configuration Example 354

Enabling Different Anti-Spam Scanning Engines in Different Mail Policies: Configuration Example

355

Protecting Appliance -Generated Messages From the Spam Filter 357

Headers Added During Anti-Spam Scanning 357

Reporting Incorrectly Classified Messages to Cisco 358

How to Report Incorrectly Classified Messages to Cisco 358

How to Report Incorrectly Classified Messages to Cisco 359

Using Cisco Email Security Plug-In 360

Using Cisco Email Submission and Tracking Portal 360

Forwarding Incorrectly Classified Message as an Attachment 361

How to Track Your Submissions 362

Determining Sender IP Address In Deployments with Incoming Relays 362

Example Environments with Incoming Relays 363

Configuring the Appliance to Work with Incoming Relays 364

Enabling the Incoming Relays Feature 364

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Adding an Incoming Relay 364

Message Headers for Relayed Messages 366

How Incoming Relays Affect Functionality 369

Incoming Relays and Filters 369

Incoming Relays, HAT, SBRS, and Sender Groups 370

Incoming Relays and Directory Harvest Attack Prevention 370

Incoming Relays and Trace 370

Incoming Relays and Email Security Monitor (Reporting) 370

Incoming Relays and Message Tracking 370

Incoming Relays and Logging 370

Configuring Logs to Specify Which Headers Are Used 371

Monitoring Rules Updates 371

Testing Anti-Spam 372

Sending an Email to the Appliance to Test Cisco Anti-Spam 373

Testing Anti-Spam Configuration: Example Using SMTP 373

Ways Not to Test Anti-Spam Efficacy 374

Outbreak Filters 375

CHAPTER 16

Overview of Outbreak Filters 375

How Outbreak Filters Work 375

Delaying, Redirecting, and Modifying Messages 376

Threat Categories 376

Virus Outbreaks 377

Phishing, Malware Distribution, and Other Non-Viral Threats 377

Cisco Security Intelligence Operations 377

Context Adaptive Scanning Engine 378

Delaying Messages 378

Redirecting URLs 379

Modifying Messages 380

Types of Rules: Adaptive and Outbreak 380

Outbreak Rules 380

Adaptive Rules 380

Outbreaks 381

Threat Levels 381

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Guidelines for Setting Your Quarantine Threat Level Threshold 381

Containers: Specific and Always Rules 382

How the Outbreak Filters Feature Works 382

Message Scoring 383

Dynamic Quarantine 383

Outbreak Lifecycle and Rules Publishing 384

Managing Outbreak Filters 385

Configuring Outbreak Filters Global Settings 386

Enabling the Outbreak Filters Feature 386

Enabling Adaptive Rules 387

Enabling Alerts for Outbreak Filters 387

Enabling Logging of URLs and Message Tracking Details for URLs 387

Outbreak Filters Rules 388

Managing Outbreak Filter Rules 388

The Outbreak Filters Feature and Mail Policies 389

Setting a Quarantine Level Threshold 390

Maximum Quarantine Retention 390

Bypassing File Extension Types 390

Message Modification 391

The Outbreak Filters Feature and the Outbreak Quarantine 393

Monitoring the Outbreak Quarantine 393

Outbreak Quarantine and the Manage by Rule Summary View 394

Monitoring Outbreak Filters 395

Outbreak Filters Report 395

Outbreak Filters Overview and Rules Listing 396

Outbreak Quarantine 396

Alerts, SNMP Traps, and Outbreak Filters 396

Troubleshooting The Outbreak Filters Feature 396

Reporting Incorrectly Classified Messages to Cisco 396

Multiple Attachments and Bypassed Filetypes 397

Message and Content Filters and the Email Pipeline 397

Protecting Against Malicious or Undesirable URLs 399

CHAPTER 17

URL-Related Protections and Controls 399

User Guide for AsyncOS 12.5 for Cisco Cloud Email Security - GD (General Deployment)

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Cisco Cloud Email Security User guide

Brand: Cisco

Model: Cloud Email Security

Category: Software

Type: User guide

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Cisco Cloud Email Security User guide

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