Email NDR

This is the NDR that a someone gets trying to send my client an email; they were kind enough to send me their NDR:
The following recipient(s) cannot be reached: on 4/20/2010 7:02 PM
            The e-mail system was unable to deliver the message, but did not report a specific reason.  Check the address and try again.  If it still fails, contact your system administrator.
            < #5.0.0 smtp; 5.4.7 - Delivery expired (message too old) [Default] 451-'4.7.0 Timeout waiting for client input' (delivery attempts: 24)>
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What email system are you running?
redesystemsAuthor Commented:
exchange 2007 via sbs 2008
redesystemsAuthor Commented:
I have run both domains through mxtoolbox an all seems okay with the exception of my client reporting the following warning on likne 3:

 Not an open relay.
 0 seconds - Good on Connection time
 5.351 seconds - Warning on Transaction time
 OK - resolves to
 OK - Reverse DNS matches SMTP Banner
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Is only one sender having trouble sending you messages?
This similar ex-ex issue discusses a similar problem in which the sending server was having MTU issues
redesystemsAuthor Commented:
I have forwarded a message and received a 4.4.7 error now as well.  It seems only when there are attachements that the file fails to go through.
Please check your attchment file size for inbound message limit.
redesystemsAuthor Commented:
I have changed the size to the maximum  and have sent a test message from the mail server which took less than 30 seconds for me to receive.  I then replied to the message and still after 7 minutes have not received it on the email server.
Please try this from the Internet i.e. not on your client's LAN:

from a command prompt type (enter at the end of each line):
nslookup -type=mx
 (note the fqdn of their mail server)
telnet fqdnoftheirmailserver 25
rcpt to:

Does it say message was queued? Or did you get an error somewhere? Give us the output please.
redesystemsAuthor Commented:
on mail from: emailaddress (valid one used)
501 5.1.7 invalid address
redesystemsAuthor Commented:
Seems like the problem was with the content filter - I disable that part (SPAM filter) and messages seem to be going through okay - SPAM and all....

thanks - I will keep open until I know for sure that this resolves the issue.

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Looks like I messed up instructions, there should be a space after mail from:
Looks like you caught it and entered it correctly..
Did you chack this out? "3rd Party Application or Mail Server May Fail to Send To or Relay Mail Through Exchange Server 2007"
redesystemsAuthor Commented:
the default domain entry was blank so I added it as per kb article
will post further develeopments

Ady FootSharePoint ConsultantCommented:
This question has been classified as abandoned and is being closed as part of the Cleanup Program.  See my comment at the end of the question for more details.
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Email Protocols

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