Exchange 2010 "poisoned Queue"

A user have told me that someone has sent her an email and she hasnt received it. i check he queue o exchange and i have noticed that there are around 100 emails in queue folder called "Poisoned"
I have selected all emails ....right clicked and resumed them

after that some users received email that were around 1 week old.

why did it happened ?  
how can prevent it from happening again without checking queues ll the time ?

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MichaelVHConnect With a Mentor Commented:
In a nutshell: poisoned messages are messages that are potentially harmful for Exchange.

They got there because Exchange determined they could be harmfull or they did crash the Exchange server in any way.
Checking these queues is part of the Exchange Admin job ;-)

Please read here for more information:

aucklandnzAuthor Commented:
Thanks for your reply.

Is it possible to find out the cause to why email ends up poisoned and suspended ? when i resume suspended email it gets thru.
AFAIK not.
Exchange will not even tell you that there are messages in the queue, you have to monitor it by yourself.

Basically, Exchange will move message there if it has troubles processing it (server failure) and that might be for various reasons (bad agent,...)

aucklandnzAuthor Commented:
Thanks for you help
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