The ServerGrove blog has a recent post for the Symfony2 users out there, showing how you can spool emails on a VPS/shared hosting using SwiftMailer and the Symfony2 bundle to interact with it.

When you send an email, the mailer communicates with a remote server in charge of receiving the message and of delivering it to the recipient. This process can cause your form to submit slowly as it depends on how fast the mail server responds. Spooling allows us to decouple the application execution line from the process of the sending one, two, or as many emails as we need.

They show you how to configure the SwiftMailerBundle with the mail server's settings, how to set up the command to send the emails and the settings you'll need to put in your cron file to run the "send" operation periodically.