You'd probably want to use a service like Postmark[1] or Mailgun[2] or Mailnuggets[3] for that as they already exist and are built for that sort of thing. They can handle attachments and the like too. They're simple enough to use depending on what you want to do, although if you just want to use "if email is to support@domain.com forward to crm@otherdomain.com" you could use gmail filters on their own.

[1] http://postmarkapp.com/inbound [2] http://mailgun.com [3] http://mailnuggets.com