TLDR: I want to replace Thunderbird as a IMAP, CalDAV & CardDAV-Client, mainly under Windows, Linux & Mac optionally. I'm looking for a software to replace Thunderbird, I need at least the following features:
- Calendar with CalDAV support (online is enough, offline sync not needed)
- Address book with CardDAV backend (online is enough, offline sync not needed)
- Several IMAP/SMTP accounts
- Windows, Linux and OSX optional
- Open Source prefered, but closed and payware is not excluded
At the moment we run a SOGo server (CardDAV, CalDAV) with Thunderbird as Clients. Thunderbird with Lightning and the SOGo plugins provides CalDAV and CardDAV, but we often experience problems with the sync and need to fix it manually. Also it seems that sync updates in the background halt the whole Thunderbird, you cannot even continue to write an email.
The somewhat stale development and unsure situation (does it stay with Mozilla?) aren't that attractive as well.