Mozilla Thunderbird

Free and open-source ¹ email client that also functions as a personal information manager with a calendar and contactbook, as well as an RSS feed reader, chat client (IRC/XMPP/Matrix), and news client.
— Mozilla Thunderbird - Wikipedia

Since thunderbird support all organizing and email related features, I use it as all-in-one email client, plus it’s open-source and now have mobile clients.

Actual shortcuts and main features aviable in thunderbird documentation ².

References

Footnotes

1. Linux Build Prerequisites ↩

2. Keyboard shortcuts ↩