2. Wrong Username

If the user part of the email address (the bit before the '@' sign) is not recognised by the remote system, then the error message you get back will depend on the client you are using and whether the domain you are emailing is an Oxford domain or not.

If you use and IMAP client, the error will always look something like this:

This message was created automatically by mail delivery software.
	  A message that you sent could not be delivered to one or more of its recipients. 
	  This is a permanent error. The following address(es) failed:
	  SMTP error from remote mail server after RCPT TO:<no-one@bbc.co.uk>:
	      host cluster1.eu.messagelabs.com []:
	      550 Invalid recipient <no-one@bbc.co.uk> (#5.1.1)

If you use OWA or Outlook and domain you are emailing is not an Oxford domain, the error will look as above. If it is a domain that does belong to Oxford it will look something like this:

          Delivery has failed to these recipients or distribution lists:
          Examine the text below for diagnostic information returned from the remote server. 
          If you have further problems then please contact help@oucs.ox.ac.uk.
          The following organization rejected your message: relay5.mail.ox.ac.uk.
          Sent by Microsoft Exchange Server 2007 
          Diagnostic information for administrators:
          Generating server: exht01.ad.oak.ox.ac.uk
          relay5.mail.ox.ac.uk #550-RPT-UNK: Recipient unknown. 
          Search at http://www.ox.ac.uk/contact/ 
          550 http://www.oucs.ox.ac.uk/network/smtp/relay/index.xml?ID=errors#rpt-unk ##

The same reasons for possible failure apply as for errors with the site part - mis-typing or transcription, incorrect original reference and the username no longer being valid. Again, if you can spot the problem immediately, simply re-send the message with the correct address. If not, then you will need to go back to your original source.

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