If you tell them .. buy an app or setup some services .... they ask "how much more does it cost than using a Googlemail-domain?"! .. and they often decide for google. Most companys around 100 employees don`t worry about ownership of their "own " mailserver. They outsource all this within some days.
All new features, new clients-interfaces for desktops are not requested by my cutomers. They get confused about all these names. Most of them just want to send and receive email, track their appointments and nothing more. Keep interfaces simple and they like it. Maybe you could give icons a new fresh design every 5-10 years.. that´s it.
..but give them every 2 month a Mobile-Device-Update so they can connect the new, cheap devices they buy twice a year...please!