Microsoft Exchange 2007 Catch all Transport Agent

This is a little tutorial about how to install a Microsoft Exchange Catch All Agent / Mailbox. ‘Catch all’ is the ability of an SMTP server to redirect messages to non-existing recipients to a specific address. For example, your domain is like Someone sends an email to and you don’t have a mailbox with the corresponding email address, the email can’t be delivered. The sender get’s a notification (NDR – Non Delivery Receipt,  STMP RFC Error Code 550) similiar to this one:

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
SMTP error from remote mail server after RCPT TO:<>:
host []: 550 No Such User Here

If you want your Microsoft Exchange Server to take such mails and put them in a common mailbox, you could use the nice Microsoft Exchange 2007 Transport Protocol Agent which provides the (MTA) catchall functionality from Wilbert De Graaf. The Agent is Open Source published on To download the Agent, click here and click on download..

Setup is quite easy.

The instruction has been taken from the install notes from Wilbert de Graaf..
CatchAllAgent: Exchange 2007 Transport Protocol Agent

CatchAllAgent is an Exchange 2007 Transport Protocol Agent. If a message comes in, and a
recipient of that message does not exist (unknown recipient), the recipient typically gets
rejected by the Recipient Filtering feature (which is also a Transport Protocol Agent).
The CatchAllAgent can be configured to rewrite the recipient address for unknown recipients
such that such messages end up in a dedicated mailbox. The configuration allows for multiple
domains, but you can only specify a single target address for each of those domains.

The configuration is called config.xml and should be found at the same location of the agent’s
assembly (DLL). The contents looks something like this:

This says that messages to unknown recipients @ should be redirected to
“”, and messages to unknown recipients @ should be
redirected to “”. Recipients that are either known at those domains,
or at other domains (either known or unknown) are unaffected.
Changes to the configuration file will be picked up on the fly. If there is an error
in the configuration file, the (new) content will be ignored.

Installation Steps
1. Create a directory on your Transport server (either Edge or Internet Facing Hub role)
2. Unzip the file in that directory
3. Edit the config.xml according to your needs
4. Open the Exchange 2007 Management Shell and run the following command to install
the agent, assuming the directory with the CatchAll agent is c:\catchallagent:
[PS] C:\catchallagent>install-transportagent -Name "CatchAll Agent" -TransportAgentFactory:CatchAll.CatchAllFactory -AssemblyPath:"C:\catchallagent\CatchAllAgent.dll"
Identity Enabled Priority
——– ——- ——–
CatchAll Agent False 18
WARNING: Please exit Powershell to complete the installation.
WARNING: The following service restart is required for the change(s) to take effect : MSExchangeTransport
5. Now the priority of the CatchAllAgent needs to be smaller that the priority of the Recipient
Filtering agent. So you first need to figure that out using the get-transportagent task:
[PS] C:\catchallagent>get-transportagent
Identity Enabled Priority
——– ——- ——–
Transport Rule Agent True 1
Journaling Agent True 2
RMS Encryption Agent False 3
AD RMS Prelicensing Agent False 4
Connection Filtering Agent True 12
Content Filter Agent True 13
Sender Id Agent True 14
Sender Filter Agent True 15
Recipient Filter Agent True 16
Protocol Analysis Agent True 17
CatchAll Agent False 18

So in this case (Internet facing Hub) the priority of the Recipient Filtering Agent is 16, and since
11 is available, that’d be a good pick. Use the following command to set the priority:
[PS] C:\catchallagent>set-transportagent "CatchAll Agent" -Priority:11
WARNING: The following service restart is required for the change(s) to take effect : MSExchangeTransport
6. Now the agent can be enabled:
[PS] C:\catchallagent>enable-transportagent "CatchAll Agent"
WARNING: The following service restart is required for the change(s) to take effect : MSExchangeTransport
7. Restart the Transport service:
net stop MSExchangeTransport
net start MSExchangeTransport

The agent supports standard .NET tracing. To enable tracing, you have to add the following
section to the application configuration file (edgetransport.exe.config):

initializeData=”traces.log” />

The result is that traces will be written to file “traces.log” in the applcation’s directory.
There will only be traces for configuration changes, and not when a recipient gets processed.


CatchAllAgent for Microsoft Exchange 2007 Transport Protocol Agent on

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