Unable to send mail to external domain mail id's RRS feed

  • Question

  • We have a dot net application which send mail via Exchange Server 2010 using SMTP client, Everything working fine when we send mail with in same domain but throws an error "5.7.1 Unable to relay " when we try to send mail to external domain email address.

    At same time Outlook client can easily send mail to internal or external domain via same Exchange Server 2010.I am unable to figure out what is the cause of this discrimination ?

    Also like to add faced same relay error when I tried to send mail via telnet utility to external domain mail id.

    • Edited by Pkalia Friday, September 28, 2012 6:54 AM
    Friday, September 28, 2012 6:53 AM


  • Exchange isn't "open relay", which mean unauthenticated user cannot send email to outside domain, they can only send mail to accepted domain.

    You need either to allow your application to authenticate, or configure a special receive connector that allow relaying and allow your application IP on the connector.

    You have a full explanation of the relay connector here :, as for the authenticating, you can check the relevent RFC :

    • Proposed as answer by Castinlu Monday, October 1, 2012 5:24 AM
    • Marked as answer by Castinlu Friday, October 5, 2012 1:37 AM
    Friday, September 28, 2012 7:01 AM