Best method for emailing 1000+ a day?

[Sykoi]

I'm about to start on the newsletter part of my site, however I'm unsure of how I want to manage this. I was thinking about having an e-mail queue, in which twice a day a task fills with the emails to be sent out based on a user's setting...

However I don't quite know how to send these e-mails out, how often, or how many at once... Whats a good number at a time? 100? 200? 250? What about how often? Every few minutes? And finally, what exactly is the best way to send these out? Just use php's mail() function?

I really need to find the best method of doing this, and while I will be testing - it would be nice to get some input from anyone who has faced this problem in the past.

[bradgrafelman]

Quote from the [man]function.mail[/man] page:

Note: It is worth noting that the mail() function is not suitable for larger volumes of email in a loop. This function opens and closes an SMTP socket for each email, which is not very efficient.

For the sending of large amounts of email, see the PEAR::Mail, and PEAR::Mail_Queue packages.

[MarkR]

I don't believe this part of the documentation is particularly accurate, as it applies only to the windows (SMTP) method of sending.

Sending loads of mails in a loop should be fine, especially if you put some sleeps in to slow it down (gives some of the earlier ones a chance to be delivered).

A decent MTA will batch them by destination anyway, and retry as necessary.

Of course using a cron job for this is pretty much vital, as it mustn't be interrupted (perhaps do it at a time of day when the machine will be less busy).

Of course you could store some data in the database about who is to receive what- depending on your requirements.

Mark