Have a Microsoft Exchange Server delivering to an IIS SMTP Service that hosts a particular domain.
This domain is smsmaker.com, hosted on an IIS SMTP Service, with GFI SMSMaker running on that server picking up the emails, and then sending them via a mobile modem as SMS'.
Any user in the exchange system should be able to send to firstname.lastname@example.org, but unless that number/email address in the list, the SMS should not be sent.
We want to have a restricted list of mobile numbers (or email addresses, however you want to put it) that can be accessed, ie our staff with company mobiles only.
Had a quick look on GFI site, and Microsoft site, and couldn't find anything.