I have more than 1M users which i need to send newsletters to. I have tried PHPList but it has failed as it gets stalled after every 30K emails. I need a faster and more reliable solution.
The most affordable approach is to have an MTA SW, that will handle its own mail queues.
Your script has to connect to a local MTA (ssmtp, postfix, exim or whatever you prefer) this one will hand mails for you.
Your task is only to send a mail to N recipients, not to send it on the net by your own. Make someone being designed to do this task to do its job :)