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Exchange 5.5 email bounce issue

By ReMaind ·
I've been having this problem for a while now:

This one company repeated at random times gets this error when trying to email a few different people in my company:

===== Original Message from at 4/28/04 12:48 pm
>An error occurred sending a message to:
>Relay host reported error: (
>550 5.1.1 <>... User unknown
>Original Message Follows:
>Reporting-MTA: dns;
>Remote-MTA: dns;
>Final-Recipient: rfc822;
>Action: failed
>Status: 5.0.0
>Last-Attempt-Date: Wed, 28 Apr 2004 12:48:34 -0400

our user is definitely a user with no problems receiving mail from anyoneone else, the accounts that their user CAN send to in our domain are no different in configuration than the ones he CAN'T send to (aside from the obvious).

This has been happening on and off for weeks, and we are concerned that other people may have been getting this error and haven't been notifying us or haven't been able to.

thanks in advance

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by ReMaind In reply to Exchange 5.5 email bounce ...

Point value changed by question poster.

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by mikex In reply to Exchange 5.5 email bounce ...

550 error expalantion:

Generic protocol error (SMTP error). The remote SMTP response to our EHLO with a 500 level error and the sending system will QUIT the connection and report this with NDR indicating the remote SMTP server cannot handle the protocol. (For example, if a Hotmail account is no longer active, a 550 SMTP error will occur.)

Error 500 - 550 related expalanation:

All numeric codes that were first available with Exchange 2000 Service Pack 1 (4.3.2, 5.4.0, 5.4.4, and 5.5.0) were classified as 5.0.0 in Exchange 2000 Service Pack 1 and earlier.

Possible Causes:
There is no route for the specified address space. For example, an SMTP connector is configured, but this address does not match.
DNS returned an authoritative host that was not found for the domain.
The routing group does not have a connector defined. Mail from one server in one routing group does not have a route to another routing group.
An SMTP protocol error occurred.
Correct the address space, or add an address space of type SMTP with asterisk (*) value to one or more SMTP connectors.
Verify that DNS is working correctly.
Make sure that the routing groups have connectors that connect them.
If you are running Exchange 2000 without Service Pack 1, apply Service Pack 1 to help determine the actual issue.

And one more - very simple but often a serious reason: Check the particular PC network cables/jacks/wall jacks

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