I want to tell my experience.
I don't think it depends on the fact that outlook has something extra.
I think it depends on the laziness of the users to see an interface other than outlook
Honestly I can't understand what has more outlook than emclient for example
I forced my collaborators to use emclient and after the initial protests and a bit of use nobody had anything to say anymore
Sabatino Traini
Chief Information Officer
Genial s.r.l.
Martinsicuro - Italy