Delivery SMTP Receive Connector Test

Receive connectors control the flow of inbound messages to your Exchange organization. They are configured on computers running Microsoft Exchange Server 2013/2016 with the Transport service, or in the Front End service on a Client Access server.

Each Receive connector listens for inbound connections that match the settings of the Receive connector. A Receive connector listens for connections that are received through a particular local IP address and port, and from a specified IP address range.

When you install a Mailbox server running the Transport service, two Receive connectors are created. No additional Receive connectors are needed for typical operation, and in most cases the default Receive connectors don't require a configuration change. These connectors are the following:

  • Default <server name>   Accepts connections from Mailbox servers running the Transport service and from Edge servers.
  • Client Proxy <server name>   Accepts connections from front-end servers. Typically, messages are sent to a front-end server over SMTP.

When mail delivery slows down or when too many mails are returned undelivered, administrators should be able to rapidly identify the connector responsible for this, so that they can figure out how such connectors can be reconfigured to avoid the slowness or the message rejections. To determine this, administrators can use the Delivery SMTP Receive Connector test. This test auto-discovers the default and user-configured SMTP receive connectors on the Exchange server. For each discovered connector, the test reports the incoming load on the connector, the rate at which each connector processed the load, and the count of mails rejected by the connector. In the process, the test points to  overloaded connectors, slow connectors, and the ones that rejected a vast majority of emails, so that administrators can fine-tune the problematic connectors and minimize the anomalies.

Target of the test : An Exchange 2013/2016 server

 Agent deploying the test : An internal agent

Outputs of the test : One set of results for each SMTP receive connector

Configurable parameters for the test
  1. Test period - How often should the test be executed
  2. Host - The host for which the test is to be configured.
  3. port – The port at which the host listens.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Data received rate:

Indicates the rate at which email data was received by this connector.


In the event of a slowdown, you can compare the value of this measure across connectors to know which connector is processing emails slowly.  

Inbound connections to receive connector:

Indicates the current number of inbound connections to this connector.


Compare the value of this measure across connectors to know which connector is being used the most. Overloaded connectors can thus be identified. You may want to configure additional connectors to ensure that load is uniformly balanced across connectors.

Messages received by receive connector:

Indicates the rate at which messages are received by this connector.



Messages rejected due to size restriction:

Indicates the number of messages that were rejected by this connection due to size restriction.


Ideally, this value should be 0. A non-zero value implies that one/more messages have been rejected owing to violation of size limits. You can apply limits to messages that move through the Microsoft Exchange Server 2013/2016 organization. You can restrict the total size of a message or the size of the individual components of a message, such as the message header, the message attachments, and the number of recipients. You can apply limits globally for the whole Exchange organization, or specifically to a connector or user object. If limits applied to a connector are causing too many messages to be rejected, identifying the connector with the maximum rejections will lead administrators to that connector for which message size restrictions have either to be lifted or fine-tuned.