I've spent a lot of time looking into this and am as frustrated as you. I'm building out a small consulting company based on Linux, and the basis of it all - email, contacts, calendars - is a fiasco. I went to Evolution as a client, which handles all of the above. Thunderbird does mail but its contact solutions require LDAP, not CardDav and its calendar solutions are bolted on, not integral. Linux devs spent a lot of time working on the "replacement for Outlook" in the early 2000s before giving up and spending their energy blowing up Gnome2's otherwise-perfectly functioning DE instead. My two go-to solutions on Linux desktops are Evolution, as mentioned, and the web client for Fastmail, which offers email, calendaring and contact sharing. Thunderbird is behind. There's a recent new add-on that purports to deal with carddav and caldav in Thunderbird, but it's still got a rough edge or two, and annoyingly, remains an "add-on" which aesthetically sends the wrong signal. On KDE, Kontact (encompassing Kmail, Korganizer for calendars and Kontact) works very well for my techie colleagues but is a bit weird for non-technical staff. I've also looked at Zimbra and the former Zarafa (now Kopano) and Kolab and some others, and Fastmail's web client remains the easiest and friendliest solution, while Evolution remains the best desktop client capable of handling IMAP/CALDAV/CARDDAV. It's annoying though. On Windows I'd just install emClient and call it a day (and would avoid Outlook, which I desperately dislike).