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?