SMTP Diagnostics – SMTPDiag Tool

What is SMTPDiag?

SMTPDiag is a troubleshooting tool designed to work directly on a Windows server with IIS/SMTP service enabled or with Exchange Server installed.

What is it used for?

  • It utilizes the same API's as Windows and Exchange in order to diagnose configuration and connection issues involving SMTP and DNS.

  • It issues DNS queries using both UDP and TCP.

  • It checks the syntax is to check Start of Authority (SOA) for the remote address domain.

How to use it:

commandprompt:\> SMTPDIAG “sender address” “recipient address” [-d target DNS] [/v]

Argument & its definition:

sender address
: Required. Address of a local mailbox. Used to verify SMTP submission and check inbound DNS.

recipient address: Required. E-mail address of remote mailbox you are trying to send mail to. Used to verify DNS, and remote mailbox availability.

-d target DNS :Optional. IP address of target DNS server to use to look up remote MX (mail exchange) records for testing. This is configured as an external DNS server in Exchange. Please note that the external DNS setting is not available for Internet Information Services (IIS) SMTP.

/v: Optional. Displays additional information about each test.

/?: Displays Help


Please Note: The results will be color coded in the syntax. It will have the following colors and its definition:

White text indicates action being taken.
Gray indicates informational results
Green indicates a successful test result.
Red indicates a failed test result.

You can download the tool from Microsoft Download Center.

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