The full calender feature I was looking for ages in an email client, eM Client does have it!
The fast search feature: terrific! I’m just so happy I don’t have to look any further for a solution syncing multiple calendars, such a hassle in Outlook.
Autohyperlink when composing an email! (Sorry Thunderbird).
Signature for each account (such a hassle in TB),
SMTP for each account (again a hassle in TB, sorry).
Overall a very, very happy user.