SMTP Event IDs: 7004, 7010 errors

When I checked my server logs then I was seeing the following re-occuting and I want to solve or understand this issue.

Event ID: 7004
This is an SMTP protocol error log for virtual server ID 1, connection #445. The remote host "**.***.***.**", responded to the SMTP command "xexch50" with "504 Need to authenticate first ". The full command sent was "XEXCH50 2260 4". This will probably cause the connection to fail.

This is an SMTP protocol error log for virtual server ID 1, connection #446. The remote host "***.***.**.**", responded to the SMTP command "rcpt" with "550 <user@domain.com>... No such mailbox ". The full command sent was "RCPT TO:<user@domain.com> ". This will probably cause the connection to fail.

Event ID: 7010
This is an SMTP protocol log for virtual server ID 1, connection #447. The client at "213.1.119.186" sent a "rcpt" command, and the SMTP server responded with "550 5.7.1 Unable to relay for scanner.reports@bt.com ". The full command sent was "rcpt TO:scanner.reports@bt.com". This will probably cause the connection to fail.

This paticular event started at:
Time: 10.03.36
Time: 10.03.41
Time: 10.03.47
Time: 10.03.52
Time: 10.03.57

With the last event occuring at:
Time: 10.04.03

Any ideas how to solve this error? Thanks

There is an article describes delivery status notifications in Microsoft Exchange 2000 Server and in Microsoft Exchange Server 2003. Specifically, this same article describes permanent failure messages and transient failure messages that frequently become permanent delivery errors. Follow the article in this link - http://support.microsoft.com/?id=284204