Random outgoing emails getting stuck in Exchange SBS 2003

laurencoull used Ask the Experts™
Exchange 2003 SP2 running on a 2003SBS, with BT as the email host ISP.
Every time the server gets a re-boot (typically every few months), a number outgoing emails which had obviously been sticking in Exchange for many weeks then decide to go out and they get phone calls from puzzled recipients saying “I just received your email dated 31st December”, etc.
The SBS Internet Connection wizard settings initially had email set to route via mail.btconnect.com so 6 weeks ago I got a DNS address from BT and changed the Email routing method to the DNS they gave me. All appeared well until last Tuesday when the server had to be re-booted and a mass of old emails, which they believed had been sent out at the time, got sent out and reached their destinations, to the bemusement of the recipients, but also a large batch of NDRs appeared going back to the time of the server’s previous re-boot a month earlier. BT have confirmed the DNS in use is correct. I’m not sure if I should change back to route via mail.btconnect.com. Someone suggested asking BT if using reverse DNS would resolve the issue and someone suggested asking them for a Smarthost, but I’m afraid these terms are new to me and I wouldn’t know where to start or what that would change.  
A sample of some of the NDRs read:
smtp;451 Greylisting enabled, try again in 5 minutes
This message was rejected due to the current administrative policy by the destination server
smtp;451 Internal resource temporarily unavailable
smtp;421 Your address has been graylisted
The e-mail system was unable to deliver the message, but did not report a specific reason
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I would recommend a smarthost. Then all mail routes outbound through them and they manage your blacklist, to make sure you aren't blacklisted.
Alan HardistyCo-Owner
Top Expert 2011

You have discovered the 'Greylisting Bug'.  Please apply the following patch and the problem will go away:


Good Luck laurencoull
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Alan HardistyCo-Owner
Top Expert 2011

Geodash - why the good luck?


Well done alanhardisty,
I had indeed found the greylisting bug and the patch did indeed send it away!
Just before I award your points though, my manager has asked me to find out if there is any way that in the event of an email being sent in future and not reaching its recipient, the sender can be notified of this? I'm not convinced there is. (But you still get your points even if there isn't!).
Top Expert 2011
Only in the movies unfortunately!

Once the email has left your server, you have no control over it.  You can ask for a delivery receipt, but you may not get one once the message is delivered, thus you won't have a clue if it has been delivered or not and your server isn't going to start guessing if it made the trip successfully or got lost en-route.

Email is unfortunately not a guaranteed method of communication, so as long as you remember this, you / your boss shouldn't be disappointed (well - hopefully not at least).

If your server tries to send an email and can't, then it is usually configured to send a delayed delivery message to the sender after about 12 hours.  If after 3 days (or whatever you have configured on your SMTP Virtual Server), the message still can't be sent, then the sender will get a failed delivery message.  This all goes on because your server cannot send the message, but if it leaves your server, then that is the last you may ever hear of it.


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