configure SQL Server 2008 R2 to send external email

I finally got SQL Server configured so that I could send emails to users on my domain from within a stored procedure using msdb.dbo.sp_send_dbmail

but I'm currently unable to use this method to send messages to external email addresses (those outside my domain).  When I attempt to send outside my domain, I get the following error message:

The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 1 (2015-10-30T10:00:25). Exception Message: Cannot send mails to mail server. (Mailbox unavailable. The server response was: 5.7.1 Unable to relay).
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Dale FyeOwner, Developing Solutions LLCAsked:
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Dale FyeOwner, Developing Solutions LLCAuthor Commented:
BTW,  in another post, someone indicated that there is an Exchange setting which needs to be changed, but he was unsure what the setting was, and what the appropriate value is.
ste5anSenior DeveloperCommented:
You need to enable relaying. This depends on your Exchange version.

Exchange 2010 - Allow Anonymous Relay on a Receive Connector

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Are you using the local iis console 6 SMTP or are you telling SQL to use a remote SMTP server to send through?
Using the local provides the option that is under your control and has few issues.
Dale FyeOwner, Developing Solutions LLCAuthor Commented:
Thanks for your assistance.
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Microsoft SQL Server 2008

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