fortigate utm vs fortimail?

Sorry if this is an FAQ - I've not seen any posts that answered this.  I currently have a vsphere VM running sophos-utm as an SMTP spam/av proxy, and have become unhappy with the amount of junk that gets through.  I've heard good things about fortinet, but am confused by the difference (if any?) between fortimail (virtual or physical) vs fortigate with UTM license.  I am currently using a pfsense firewall, and have no inclination to switch, unless that went with switching to fortigate+utm.  I seem to get the impression that fortigate+utm is less featureful, is this true?  e.g. providing a per-user quarantine, and other things, whereas fortigate+utm would mainly just tag the messages with a SPAM header, and my MTA would sort those into junk folders (and I'm okay with doing that, if needed).  And if I went with fortimail, I'd be inclined to go the VM route, if only because I can back up the appliance easily, using veeam.  Any thoughts/tips welcome!