Question: What happens when a user sends a 1Mb e-mail to 2000 external recipients, and also requests delivery receipts?

Answer: MailSweeper delivery service will die and mail will start to queue on your server. Messages will build up in the 'domains' folders and in 'holding' as your the policy server becomes unable to deliver any more mail.

This happened to me today. It was noticed early as I use an spool watching utility (free on JMC's mswtools.org) which uses blat to send alerts when the number of files in the MSW spool directories go over certain thresholds.

According to the ClearSwift engineer I spoke to, the problem is to do with the way the delivery service can only handle 50 threads at a time. One would imagine a policy server would cope with 2000 messages being dumped on it but apparently this will just keel it over. Multiple reboots did seem to give enough short bursts to clear the 'domains' queues apart from one internal domain containing around 800 delivery receipts and 100 business e-mails. The problem was, on most of these delivery receipts and delivery failures the original message was attached, and the queue was standing at around 900Mb. This would not clear and forcing a retry seemed to make the processing just freeze up. Unfortunately MailSweeper lacks controls on this part of the homepage to delete items in the delivery queue, so to purge all of the delivery receipts I had to delete the corresponding files in the file system on the PS. The problem to overcome then is, how do you make sure you only delete the delivery receipts when the folder is full of randomly named RCP files? I used the following commands within that domain folder to achieve this:

findstr /S /M "Message relayed" *.RCP > output.txt
FOR /F %I IN (output.txt) DO del %I

Tomorrow I'll be implementing a much lower limit on the number of recipients per message that can be sent through Exchange, and of course suggesting a better method of delivering this PDF in the future. I'm thinking Morse code ...

Edit: Just found the default in Exchange 2003 is a maximum of 64000 recipients per message!

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