Just a quick warning.. Gmail/GoogleApps isn't a normal email service, If you abuse it, or they think you are abusing it, they will block you!
This is my crontab entry for Gmail polling:
# Every Ten Minutes.. Google doesn't like it if you do too many!
# Only during office-hours, Google makes you use a captcha
# if you use automated tools to access their network.. so hide in normal traffic
*/10 8-18 * * 1-5 nobody /usr/bin/php /path/to/api/cron.php
# Allow incoming on w/end.. at 30m intervals in afternoon
*/30 13-15 * * 6-7 nobody /usr/bin/php /path/to/api/cron.php
I'm thinking of setting up an email server just for osTickets and getting google to forward all tickets.. thus saving a poll request and the damn captcha hell.. users will whinge.. is not very nice.