It is perfectly possible to send out automated messages using phpmailer, but be aware that Google's tolerance may be lower than the 500-recipient limit mentioned by Gravyface. I have been using a "noreply" account to send out opt-in notifications from a web application and today I discovered that this account was suspended for abuse.
I'm pretty sure I wasn't sending out spam or hitting the daily 500 (or even 100) message/recipient limits, so be aware that Google Apps can be employing additional checks for detecting "abusive" accounts.
Addendum: I contacted the support and they re-enabled my account within the time between my original answer and this edit (w00t, Google!). Apparently, their abuse detection mechanisms are having the twitchy-trigger-fingers, but they are aware of the issue.