SMTP Connectors are in retry mode and getting transport errors

There are about 3-4 smtp connectors that are on retry and have been for a day now. The recipient gets a message back saying that:
This is an automatically generated Delivery Status Notification.

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

Delivery to the following recipients has been delayed.

not entirely sure why.  Below are also a couple of error messages in event  viewer.  Why are the SMTP connectors not working, why am I getting the following errors, and how do I fix the delayed messages?

Getting MS Exchange Transport errors Event ID# 7004
This is an SMTP protocol error log for virtual server ID 1, connection #273. The remote host "70.101.228.174", responded to the SMTP command "xexch50" with "504 Need to authenticate first  ". The full command sent was "XEXCH50 2348 3  ".  This will probably cause the connection to fail.

Also Event ID# 7010
This is an SMTP protocol log for virtual server ID 1, connection #271. The client at "70.101.228.82" sent a "xexch50" command, and the SMTP server responded with "504 Need to authenticate first  ". The full command sent was "xexch50 4308 2".  This will probably cause the connection to fail.

Thanks A Lot!
ETI2010Asked:
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PenguinNConnect With a Mentor Commented:
Check the following article http://support.microsoft.com/kb/843106
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ETI2010Author Commented:
I've verified that information and I'm still seeing stuff in retry under Queues.  Any other suggestions?
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