I have to manage multiple email accounts from different providers (IMAP and Exchange), and Thunderbird handles this effortlessly. It is completely free, open-source, and highly customizable. The local filtering rules are incredibly powerful and allow me to keep my inbox clean automatically. I also really like the new "Supernova" UI update, which makes the software look much more modern than a few years ago. Review collected by and hosted on G2.com.

Setting up calendar synchronizations (like CalDAV) can still be a bit tedious and sometimes requires add-ons or technical tinkering. It's also a desktop-only app; a native mobile version that syncs my desktop settings would be highly appreciated. Review collected by and hosted on G2.com.