I want to process a particular mailbox when it receives mail, I know I could have cron check every n minutes for any mail, but wondering if there's a way to "listen" for mail rather than continually polling.
Try a .forward file
You can pipe the message into any program or script you want, but also check if procmail can do what you want.
Depending on your mail server, it may be possible to actually have any incoming message be delivered to a process. Either in a .forward or by setting up something more advanced. In exim you can setup a transport to run a command, for certain addresses.
If you're using postfix I'd suggest aliasing the mailbox you're interested in to a process that will do the work for you. Then there's no polling. The message comes in and goes directly to being processed.
if you dont have a mail-server on your own (root-access) - you could use a web service for that: http://cloudmailin.net (200mails/month for free) - works like charme and helped me out.
来源：https://stackoverflow.com/questions/596438/trigger-a-script-when-mailbox-recieves-mail