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we have a problem on our Exchange server 2007.

I have currently 300 undelivered emails to various addresses. I'm getting this error message
421 4.4.2 Connection dropped

I checked the size of attachments and the messages aren't too big (20 KB to 6000 KB). From 200 mails to various emails addresses 137 weren't delivered.

We don't have any problems with incoming emails, but 20% of outgoing emails just sit in a queue.

Is this a DNS issue ?

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up vote 2 down vote accepted

We had a similar issue the same error but not DNS. It was caused by dropped packets over internet connection (ISP at fault). We diagnosed by setting up op manager on the public IP interface and the gateway router and see the loss. We then re routed mail to go over ADSL to see if this fixed the issue and it did. We then went to the ISP and brought it to their attention.

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thanks Johny, it was a problem with our ISP. we had a huge amount of dropped packets. – Jindrich Aug 19 '09 at 9:49

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