The price, ease of use, speed of deployment - I can't think about anything negative enough! It's been easy for us to get up and running since it was so simple from start-to-finish. We've had no issues at all using NEXXSOL as our email gateway or mail server/SPAM filter (we're working directly with their support team). They are highly responsive when we have questions regarding implementation details; they also provide excellent documentation which makes them very approachable even if you don't know much technical stuff already.