For regular newsletters, my vote is for phplist. I found this thread because I'm researching a way to throttle back product notifications. I restock in big batches due to the nature of my business. Right now, I'm about to send a batch but I wanted to know if adding
PHP Code:
sleep(x) 
into the loop would manually slow things. I don't care if it takes all night to process the notifications. I just don't want to anger the customers' hosts and get blocked.