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I've been asked to create a mailing list system which will be used to send regular newsletter type emails to our customers. The software side is just about complete, so that needs no discussion.

Having read more than once about systems getting block listed due to an outbound flood of messages I have some concerns. We have a single public IP address, so there's no way I can dedicate an address for this purpose and ending up on block lists would be quite unacceptable. We will be sending to somewhere between 1,000 and 2,000 recipients (and there will of course be an opt-out link in the message).

With that in mind, would it be safer to send the messages out in bursts of say 10, 20 or 100?, with a delay between bursts, or would it be safer to have a delay between each message?

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Thanks for the links, although neither is relevant to my case. I've run sent off a batch of nearly 1,000 in bursts of 20 with a 1 minute delay between bursts. So far (a week later) we're still clear on the block lists. – John Gardeniers Sep 20 '09 at 22:03
up vote 0 down vote accepted

Find a service that lets you use their servers for sending messages. We use a service called BigFish, we contract with Sprint, but I think Microsoft bought the service. We send our mass mail through the bigfish SMTP servers, and they have many IP addresses and deal with not getting blacklisted. That said, we still burst 20 messages at a time. We sort the messages by domain, and some cable companies block any inbound with more than a certain number of receiptants, so 20 keeps us under the threshold.

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Although this answer doesn't really address the question as asked, it's the only answer offered and therefore deserves some recognition. – John Gardeniers Aug 30 '09 at 10:39
@John, if it doesn't answer your question, you should not mark it as accepted, others are much less likely to add other answers when they see one already marked accepted – Nathan Koop Sep 20 '09 at 14:21

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