Only recently did Calendar and aliases start working reliably in the Cloudron SOGo package. I think mailbox sharing still doesn't work but it's in our TODO list.
Because of this, my personal and cloudron.io email setup doesn't use SOGo. @nebulon and I both use thunderbird for day to day use. We have a rainloop installation just to manage our mail filters (in my personal install, I use roundcube for this instead just for variety 🙂 ). This too was because thunderbird's sieve extension was previously not working with Cloudron Email. That problem has since been fixed but thunderbird's sieve extension is not very user friendly, so we stick to rainloop/roundcube. For calendar/contacts, we use our Nextcloud's caldav/carddav. Both Gnome and Thunderbird, have excellent integrations for caldav/carddav. One important consideration here is that we moved out of another provider which let us export carddav. Nextcloud has an importer that works, I haven't tested out the importers of other apps.
Shared mailboxes (like sales@, support@) was quite complicated with thunderbird (because the mail read/unread flag is not per-user). You also have to configure thunderbird to bcc replies so that the other user can see the replies. Recently, we have moved our shared mailboxes to freescout to solve this.
I don't know if this directly answers the question 🙂 I do think if SOGo was in the state it was now when we started, we probably would have used that from the get-go.
@nebulon Thanks guys, it works. Your support is good! I don't know how many people use cloudron as a private replacement of cloud services, but I think if you get all these details down and everything just works, there's a market for that 🙂