SMTP Error 5.1.2 for one user only.

Posted on 2011-05-12
Last Modified: 2012-06-22
We have around 15 users who all access Outlook via Remote Desktop on to a Server 2008 terminal server. Email is done by Exchange on SBS 2003. All users can send to one recipient except one. She gets the message below. The recipient exists at the domain, everyone else can send. This NDR is generated for this user only and happens whether we send via DNS direct from Exchange, or via the ISP's mail gateway. Does anyone know why this happens?

Your message did not reach some or all of the intended recipients.

      Subject:      test email
      Sent:      09/05/2011 14:32

The following recipient(s) cannot be reached:

      '' on 09/05/2011 14:32
            The message could not be delivered because the recipient's
destination email system is unknown or invalid. Please check the address
and try again, or contact your system administrator to verify
connectivity to the email system of the recipient.
            < #5.1.2>
Question by:plokij5006
    LVL 4

    Accepted Solution

    Try to delete recipient address from outlook autocomplete cache, and type it manually.

    Author Comment

    Your are correct, I just figured this out myself. I used NK2edit to delete the entry from the auto-complete cache file. It was in as a 'Mail to:' address instead of a SMTP address so even though it was spelled wrong it could not be sent. Well done both of us but you get the points!


    Author Closing Comment

    Good answer but didn't explain how to edit the cache file so a bit incomplete.

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