Mailspring on Linux

Good news: Mailspring runs on Linux. It's the same app you use on Windows, and TuxPick installs it for you from the Snap Store.

Mailspring

Also on Windows

A modern email app that brings several accounts into one inbox.

Installs from the Snap Store.

Press the install button above. TuxPick opens with the app already ticked. Add anything else you need.
Download the installer file.
Open a terminal with Ctrl Alt T, run the one line TuxPick shows you, and type your password when asked.

It works on Ubuntu 22.04 and 24.04, and on systems built on them like Zorin OS and Pop!_OS.