Hi when I sent mails for few users I get following NDR.  This happened for 3 or 4 users. For all other its is working fine.

For these users when I resent the same mail ,it will get delivered.  The client is outlook 2010 and configured with exchange on cloud( office 365)

From: System Administrator

Sent: Tuesday, July 16, 2013 12:28 PM

To: *******@***.co.in

Subject: Undeliverable: Report as on 16th July, 2013

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

      Subject:         Report as on 16th July, 2013

      Sent:               7/16/2013 12:28 PM

The following recipient(s) cannot be reached:

*******@***.co.in  7/16/2013 12:28 PM

            Server error: '501 5.1.3 Invalid address'

'501 5.1.3 Invalid address'

Would you receive the such error message again when you send the message through OWA?

Please manually type the email address and don't use auto-complete function in Outlook to check the result. If it would be success, please delete the name from the Auto-Complete list as the following link:

http://office.microsoft.com/en-in/outlook-help/delete-a-name-from-the-auto-complete-list-HA010355568.aspx

Tony Chen
TechNet Community Support

Hello!  I have the same problem except a different error code - just started this evening. I inadvertently removed a PST file that was associated with a live email account.  The only way I knew how to get the email address associated back to the PST file was to delete the account and then add it in again to the existing PST file.  It added fine and passed the Outlook tests and I can receive emails but when I try to send the emails I get the following System Administrator Error below.  I tried Tony Chen's suggestion to type the email address again instead of using the autocomplete and still same response.  I deleted the account again and re-added it with associating it with the existing PST file and same response, even though both times it passed the Outlook tests for sending and receiving.  Any help is appreciated!  Thank you!!

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

      Subject:    test

      Sent: 7/17/2013 12:05 AM

The following recipient(s) cannot be reached:

      '*****cox.net' on 7/17/2013 12:05 AM

            Server error: '550 5.7.1 *******cox.net... Relaying denied. Proper authentication required.'