FrontEnd SMTP Receive Connector Test

The FrontEnd SMTP Receive Connector controls the flow of inbound external SMTP traffic. When a message comes into the Exchange 2013/2016 organization from an external domain (say, the internet), the Receive connector looks for a single healthy Transport service on a Mailbox server to receive the message. Likewise, outbound messages to the internet too can routed by the Transport service on the Mailbox server to the Receive connector of the FET for Mailbox selection and delivery.

In the real world, if a single Receive connector is flooded with more messages than it can handle, delivery queues may grow longer, email delivery to internal recipients may slowdown, and critical business correspondence may not reach their destination on time. As a result, enterprises may miss out on lucrative business opportunities and related revenues. To avoid this, administrators should track the load on each FET Receive connector continuously, capture potential overload conditions and isolate the affected connectors, well before the business is impacted. This is where the FrontEnd SMTP Receive Connector test helps. For each FET Receive Connector, this test reports the count of recipients and connections handled by that connector. In the process, the test proactively captures those connectors that will probably be overloaded with messages/connections in a short while.

Target of the test : A Microsoft Exchange 2013/2016 server

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for every Frontend SMTP Receive Connector on the target server

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

Number of recipients per inbound message received:

Indicates the average number of recipients per inbound message.


Typically, the type and number of recipients determines how an FET connector operates.

  • For messages with a single mailbox recipient, the FET connector selects a Mailbox server in the target delivery group and gives preference to the Mailbox server based on the proximity of the AD site;
  • For messages with multiple mailbox recipients, the connector uses the first 20 recipients to select a Mailbox server in the closest delivery group, based on the proximity of the AD site.
  • If the message has no mailbox recipients, select a random Mailbox server in the local AD site.

A high value of this measure is therefore indicative of the average workload of the connector.

Number of new SMTP connections created:

Indicates the rate at which new connections were established by this connector to the SMTP server.


A steady increase in this value is indicative of an increase in workload.

Data received rate:

Indicates the rate at which data is received by this connector.


An above normal value for these measures over a period may indicate that the connector is overloaded.



Inbound messages received rate:

Indicates the number of messages (sent inbound into the forest) received by this connector every second.



Connections to SMTP server:

Indicates the current number of connections to this connector.


This is a good indicator of how busy the connector currently is.