Pre-Purchase question

We have 57 users with e-mail and 20 additional mailboxes. We already have a SonicWall firewall in place. My initial question is should I purchase one of their appliances or just the premium software?

The first thing I plan on doing is move our MX records from a Cloud service we are using and have it point to our internal Exchange server or an Untangle appliance. We currently have a Cloud service for our Content filtering, but will switch to Untangled after our contract expires.

Any pre-purchase advice will be greatly appreciated. :)


Thanks
J.R.
IT Director
spcaLA