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I am finding a problem sending email from my .NET application.

Server Error in '/' Application.
Mailbox name not allowed. The server response was: sorry, relaying denied from your location [X.X.X.X] (#5.7.1)

Can you please guide me?

Windows Server 2008

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Your SMTP server is not configured to permit mail-relaying. Either the IP address of your webserver needs to be put into the allowed-relays list (or whichever IP it ends up using for outbound connections), or you need to use SMTP-Auth (which will probably require SSL support as well). SMTP-Auth may be doable without having to involve the mailer-admin, you just need a viable username and password, and add the SMTP-Auth methods do your mailer routines.

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The SMTP server you are trying to user to send mail is blocking you because your IP address has either been blocked or is not explicitly allowed. Consult with the person who manages your mail server to have your IP allowed.

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If you're on Comcast or one of a few other ISPs, you'll get SMTP blocked completely unless you request it (which usually means going to business class internet). SMTP only works to their list of approved mail servers. I don't know which simply block the port and which have an open but unusable responder like this.

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