Code to stop Unable to Relay message for email

Hi
I have the code below, which works fine for sending internal email. Works on a PC.
But for external email, I get the message:
Mailbox unavailable. The server response was: 5.71. unable to relay
I've searched online, but the solutions seem to involve making changes on the exchange server. Is there a way I can add settings through code to fix this issue? 


Dim smtp As New SmtpClient("mymailservername")
Dim mailClient As New MailMessage()

  With mailClient
            .From = New MailAddress(TM_FROM)
            .To.Add(stAgent_Email)
            .Subject = stSubject
            .Body = stBody
         End With

         'send the message
         smtp.Send(mailClient)

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jdhackettAsked:
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Tony JohncockLead Technical ArchitectCommented:
Afraid you need to change the permissions on the Exchange server.

This is by design to stop viruses, rogue programs etc doing exactly this - using your server as an open relay and spamming.
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jdhackettAuthor Commented:
Ok, can you tell me how to change the permissions on the Exchange server so? Its Exchange 2010, I can't find the "SMTP Virtual Server" that the online help refers to.
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Tony JohncockLead Technical ArchitectCommented:
Here you go:

http://msexchangeteam.com/archive/2006/12/28/432013.aspx

I generally utilise a new connector.

By the way - I realise it's for 2007 but it's valid for 2010 too.
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jdhackettAuthor Commented:
Followed those instructions, added the IP of my PC, used Option 1. Still getting the same problem though. Any other ideas?
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CodeCruiserCommented:
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Tony JohncockLead Technical ArchitectCommented:
Hmm it should work - I've used it myself several times.

But i've usually granted the anonymous permission too.

Indeed, there's actually an updated article the suggests it's the preferred method:

http://technet.microsoft.com/en-us/library/bb232021.aspx

CodeCruiser - your method would bypass the Exchange server, therefore bypassing things like message tracking.
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jdhackettAuthor Commented:
Working now! I was still trying to figure it out, when I tried again and it worked. I think there must be a 10 minute delay between setting it up on the mail server and it actually working?

Either way, all good to go now, thank you.
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Tony JohncockLead Technical ArchitectCommented:
Ah good - I've never noticed a delay quite that long before but good to know you got it running :-)
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