Advanced Sender Based Routing Agent for Exchange 2019

A Microsoft Exchange 2019 Transport Agent that provides advanced sender-based routing and alias management with full support for recipient conditions and wildcard matching.

Features

• Send-As-Alias: Preserves or sets sender's alias (proxy address) in both From header and Return-Path
• Sender-Based Routing: Routes emails through specific Send Connectors based on sender rules
• Advanced Rules: Combine sender AND recipient conditions in a single rule
• Wildcard Support: Use * (any characters) and ? (single character) in all matching fields
• Per-Recipient Routing: Different routing decisions for different recipients in the same message
• GUI Configuration: Windows Forms GUI for easy rule management
• Console Configuration: Full-featured text-based configurator for Windows Server Core

Screenshots

Routing Rules

Create and manage routing rules with sender/recipient conditions and wildcards.

Test Rules

Test your rules before deployment to verify they match correctly.

Settings

Configure agent behavior and validation options.

Local Domains

Manage local domains that bypass routing rules.

Requirements

• Microsoft Exchange Server 2019 (also works with 2016)
• Windows PowerShell 5.1+
• .NET Framework 4.7.2 (for building from source)
• Exchange Management Shell must be run with Administrator rights
• User must have Organization Management role in Exchange

Quick Start

1. Build the Agent

Copy Exchange DLLs from your server to src/lib/:

C:\Program Files\Microsoft\Exchange Server\V15\Public\
  - Microsoft.Exchange.Data.Common.dll
  - Microsoft.Exchange.Data.Transport.dll

Build:

.\build.ps1

2. Install on Exchange Server

Copy the folder to your Exchange server, then in Exchange Management Shell:

.\install.ps1

3. Configure Rules

Use the GUI configurator (Desktop):

.\configure-gui.ps1

Or the console configurator (Server Core):

.\configure.ps1

Or edit routing-config.xml directly.

Configuration

Basic Rule Example

Route emails from a domain through a specific connector:

<rule name="Sales-Route"
      senderDomain="@sales.company.com"
      addressSpace="route-sales-relay.local"
      sendAsAlias="@salesteam.com" />

Advanced Rule with Recipient Condition

Route emails from sales TO partners through a specific relay:

<rule name="Sales-to-Partner"
      senderDomain="@sales.company.com"
      recipientDomain="@partner.com"
      addressSpace="route-partner-relay.local"
      sendAsAlias="@external.company.com" />

Rule with Specific Addresses

Route emails from a specific user to a specific recipient:

<rule name="CEO-to-VIP"
      senderAddress="ceo@company.com"
      recipientAddress="vip@important-client.com"
      addressSpace="route-secure-relay.local" />

Wildcard Examples

<!-- Match any subdomain -->
<rule senderDomain="*.company.com" ... />

<!-- Match specific pattern -->
<rule senderAddress="admin*@company.com" ... />

<!-- Match recipient pattern -->
<rule recipientDomain="*.mail-tester.com" ... />

<!-- Match any Gmail recipient -->
<rule recipientAddress="*@gmail.com" ... />

Configuration Settings

<settings>
  <!-- Enable/disable features -->
  <enableSendAsAlias>true</enableSendAsAlias>
  <enableSenderBasedRouting>true</enableSenderBasedRouting>

  <!-- Skip routing for internal recipients -->
  <bypassLocalRecipients>true</bypassLocalRecipients>

  <!-- Match rules against From header instead of envelope sender -->
  <routeByHeaderFrom>true</routeByHeaderFrom>

  <!-- Validate sender has alias in proxy addresses -->
  <validateProxyAddresses>true</validateProxyAddresses>
  <blockIfNoAlias>false</blockIfNoAlias>
</settings>

Logging Configuration

Enable file logging for troubleshooting and monitoring:

<logging>
  <!-- Enable/disable file logging -->
  <enableFileLogging>true</enableFileLogging>

  <!-- Log level: None, Error, Warning, Info, Debug, Verbose -->
  <logLevel>Info</logLevel>

  <!-- Custom log path (leave empty for default Exchange logs folder) -->
  <logPath></logPath>

  <!-- Maximum log file size in MB before rotation -->
  <maxLogFileSizeMB>10</maxLogFileSizeMB>

  <!-- Number of rotated log files to keep -->
  <maxLogFiles>5</maxLogFiles>
</logging>

Log Levels:

• None - No logging
• Error - Only errors
• Warning - Errors and warnings
• Info - Normal operation messages (recommended for production)
• Debug - Detailed debugging information
• Verbose - All messages including detailed tracing

Default Log Location:

C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\AdvancedSenderRouting\

Log Format:

2024-01-15 10:30:45.123 [INFO] Processing message from user@company.com
2024-01-15 10:30:45.125 [INFO] Rule 'Sales-Route' matched sender domain @sales.company.com

Rule Evaluation

• Rules are evaluated top-to-bottom (first rule = highest priority)
• First matching rule wins - no further rules are checked
• Each recipient is evaluated independently for routing decisions
• Rules without recipient conditions match all recipients

Scripts

Script	Description
build.ps1	Compiles the agent DLL from source
install.ps1	Installs and enables the transport agent
uninstall.ps1	Removes the transport agent
configure.ps1	Console-based configuration manager (Server Core)
configure-gui.ps1	GUI configuration manager (Desktop)

Project Structure

sithTA/
├── README.md
├── LICENSE
├── build.ps1
├── install.ps1
├── uninstall.ps1
├── configure.ps1
├── configure-gui.ps1
├── routing-config.xml      # Configuration file
│
└── src/
    ├── SenderRoutingAgent.csproj
    ├── SenderRoutingAgent.cs
    ├── SenderRoutingAgentFactory.cs
    ├── Configuration/
    │   └── RoutingConfig.cs
    └── lib/                 # Copy Exchange DLLs here
        ├── Microsoft.Exchange.Data.Common.dll
        └── Microsoft.Exchange.Data.Transport.dll

How It Works

Send-As-Alias

When a user sends email using an alias (proxy address), Exchange normally rewrites the From header to their primary SMTP address. This agent:

1. Detects when sender is using an alias
2. Sets the From header (P2) to the alias address
3. Sets the Return-Path/MAIL FROM (P1/envelope sender) to the alias address
4. Optionally validates the user has the alias in their proxy addresses

Note: Both the From header and Return-Path are updated to ensure consistent sender identity and proper SPF alignment when using alias domains.

Sender-Based Routing

Exchange routes outbound email based on recipient domain. This agent:

1. Intercepts messages after recipient resolution
2. Matches sender/recipient against configured rules (with wildcard support)
3. Overrides routing to use a specific Send Connector's address space
4. Supports per-recipient routing decisions (different recipients can use different routes)

Advanced Rules

Rules can specify both sender AND recipient conditions:

• Sender conditions: senderDomain or senderAddress
• Recipient conditions: recipientDomain or recipientAddress (optional)
• If no recipient condition is specified, the rule matches all recipients
• All fields support wildcards (* and ?)

Troubleshooting

Check Agent Status

Get-TransportAgent "Advanced Sender Based Routing Agent"

View Logs

File Logs (recommended):

Enable file logging in configuration for detailed troubleshooting:

# View latest log entries
Get-Content "C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\Logs\AdvancedSenderRouting\AdvancedSenderRouting.log" -Tail 100

# Or use the configurator
.\configure.ps1       # Option 5 > View Log
.\configure-gui.ps1   # Logging tab > View Log

Event Log:

# Application log
Get-EventLog -LogName Application -Source MSExchangeTransport -Newest 50 |
    Where-Object { $_.Message -like "*AdvancedSenderRouting*" }

# Or in Event Viewer:
# Windows Logs > Application > Filter by Source: MSExchangeTransport

Restart After Config Changes

Restart-Service MSExchangeTransport

Common Issues

From header not changing:

• Enable file logging with Debug level to see detailed processing
• Check sendAsAlias format: use @domain.com or user@domain.com
• Verify validateProxyAddresses setting
• Check log files for "Send-As-Alias" entries

Routing not working:

• Enable file logging with Debug level to see rule matching
• Verify Send Connector exists with matching address space
• Check if recipient is in local domains (bypassed by default)
• Use the "Test Rules" feature in the configurator to debug

Wildcards not matching:

• Ensure pattern format is correct (e.g., *.domain.com not *domain.com)
• Use the "Test Rules" feature to verify pattern matching
• Enable Verbose logging to see detailed pattern matching

Log files not appearing:

• Verify enableFileLogging is set to true
• Check the configured log path exists and is writable
• Restart MSExchangeTransport service after config changes

License

MIT License - See LICENSE file for details.

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Submit a pull request

Support

For issues and feature requests, please use the GitHub Issues page.