One of my clients recently requested a bulk mailing to their opted-in fan email list.
I timed one of the mailings, and it came to almost thirty two hours to send approximately fifty thousand emails.
It could have been done much faster, but I preferred sending it that way. Its much easier to manage and monitor. To accomplish this, I used PHP / PEAR's Mail class, and issued a sleep command of two seconds between each single email getting sent out.
I'm quite pleased to learn that PHP can run for thirty two hours and exit successfully. Cool!