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Exchange 2007 Error 421 4.2.2 Connection Dropped

Dear Experts

We currently operate in an Exchange 2007 environment with roughly 1000 users with mailboxes. However one particular user sometimes gets the following error:

Delivery is delayed to these recipients or distribution lists:
- list of recipients

This message has not yet been delivered. Microsoft Exchange will continue to try delivering the message on your behalf.

When i check the Queue Viewer i see the message with the following error:
421 4.2.2 Connection dropped

Around 1-2 days later the email will eventually send out to the recipients but really the hold up shouldn't happen at all. Again this problem is only affecting one particular user so it makes me think that the whole exchange setup etc is fine..

Hope someone can help shed some light on why this is going on

The only other thing that might be of help is that the user sends to quite a lot of receipients e.g. this particular email was sent to internal people and around 150 external addresses.. but i would have thought that this amount is not too big for exchange to handle or would i be wrong?
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Bladey001
Asked:
Bladey001
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2 Solutions
 
overdrive79Commented:
That sounds like they are sending to a recipient who is using an obscure rbl that is delaying your email delivery.  

Go to www.mxtoolbox.com and select the "blacklists" tab
type in your public ip address and let it check for a blacklisting.
I don't think you have a reverse dns problem or you would have more than one user with delivery delays.  
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Bladey001Author Commented:
Our external ip for smtp is on no blacklists, besides we use Mimecast (external hosted mail filtering service) for incomming and outgoing mail
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overdrive79Commented:
so if you are smarthosting your outbound mail to mimecast it is possible that their scanners are delaying the user's email if it is being sent to too many recipients at once or is too large.  

Also don't rule out blacklisting.  If you route your mail through mimecast it could be their servers getting blacklisted.
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MesthaCommented:
If you are routing your outbound email via a service provider and you see the message in your queues, then you need to ask your service provider why they are dropping that connection. No one else is involved here - no blacklisting or anything like that. It is purely between you and the service provider.

Simon.
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