Using Pipelining in SMTP to check email addresses does not function correctly when you disable the tarpitting functionality on a Receive connector in an Exchange Server 2010 environment


Consider the following scenario:

  • You have a Receive connector that is configured for a HubTransportserveror for an Edge Transport server in a Microsoft Exchange Server 2010 environment.

  • You disable the tarpitting functionality on this receive connector.

  • You enable Pipelining in Simple Mail Transfer Protocol (SMTP)

  • A mail service uses Pipelining in SMTP to check the email addresses before forwarding mails between internal systems.

In this scenario, the Receive connector does not reply with the expected response. Therefore, the behavior makes the mail service assumes that the email addresses are incorrect.


To resolve this issue, install the following update rollup:

2529939 Description of Update Rollup 3 for Exchange Server 2010 Service Pack 1


To work around this issue, try one of the following methods:

  1. Configure the tarpit interval to 1 if the mail service uses Pipelining in SMTP.

  2. Turn off Pipelining in SMTP.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about tarpitting functionality, visit the following Microsoft website:

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