If you’re coding an application which has to send out a high volume of emails from the site, PHP’s built in mail function is not the way to go. PHP’s mail function is resource hungry and even a low to medium load of mails could bring your server to a crawl.

Here’s another solution to look at : Swift is a fully OOP Library for sending e-mails from PHP websites and applications. It does not rely on PHP’s native mail() function which is known for using high server resources when sending multiple emails. Instead, Swift communicates directly with an SMTP server or a MTA binary to send mail quickly and efficiently.

Swift is comparable to PHPMailer except that it implements an extremely flexible and innovative plugin system meaning you can get the most out of sending emails from your PHP applications. The interface for Swift is both tighter and more intuitive.

Link: Swift Mailer – A Pluggable PHP Mailing Library