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I have been asked to send about 6500 e-mails to addresses in a member database. I have written the program, that sends and reports the ones that couldn't send etc. But my concern is that this program will just call smtpclient.Send(); and I don't know what happens if 6000 mails are in the queue. Server is MS Exchange as I have been told.

Note: I am planning to send them, say 500 by 500. But what if an exception occurs on the Exchange server at 120... then what happens to the other ones..

I will appreciate little insight to the subject.

Thanks in advance.

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Well, here is the deal. Exchange will take your emails and queue them. Depending how good you send, it will come to a grinding halt to swallow the amount of stuff you dump into it (I wrote such a sending tool once, using 64 threads, dumping them in as fast as possible as was the specs, and it stopped the exchagne serve WHILE I was sending).

Then it will start sending them.

At a later stage, you get the NDR (non delivery reports) to the origin email. This will take up to 2 days, as exchange tries to send and send again (admin setting, 2 days is standard and that one makes sense).

that sends and reports the ones that couldn't send etc.

How does that work, given that exchagne will accept ANY VALID EMAIL without checking whether it can be delivered at this time?

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uhm, that is only catching the exception in .net, whether e-mail is in a correct format etc. I will also make sure it does not send to the ones that deactivated membership and so. There is no return/response from exchange server. Can I do that?? – Emre Mar 18 '10 at 12:03
Yes, but you need to basically get the NDR (non delivery reports) after some time and priocess those, too. Like emails getting deactivated without people telling you (unsubscribing). Domains falling out ot service etc. – TomTom Mar 18 '10 at 12:16
ok thanks a lot ... so I can't get a real time response from the server and proceed accordingly – Emre Mar 18 '10 at 12:21
No. Email is a store and forward protocol, so all that the server confirms is that e got an email he accepts at THIS point and will further process. – TomTom Mar 18 '10 at 12:50

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