Roundcube [1] does a good attempt of mimicking the likes of Thunderbird, Rainloop [2] has a more 'modern' look and might appeal more to those looking for such.

Roundcube [1] does a good attempt of mimicking the likes of Thunderbird, Rainloop [2] has a more 'modern' look and might appeal more to those looking for such. [1] https://roundcube.net/ https://roundcube.net/ [2] https://www.rainloop.net/ https://www.rainloop.net/