We will be migrating from Exchange 2010 SP3 to Office 365 in the near future.
We currently use "Mail Contacts" with SMTP addresses to send mail to an internal address in our global address list and have it forwarded to an external recipient. This is accomplished by creating a Mail Contact with an external SMTP address. An actual example: We have an internal "Help IT" e-mail address in our global address book. When a help request is sent to that address, it is automatically forwarded to a Mail Contact SMTP address so that it's delivered to our Salesforce Case queue.