I use SnappyMail. It's a fork of Rainloop that's actually maintained.

https://github.com/the-djmaze/snappymail

And unlike Rainloop, the Sieve filter editor actually works.

Roundcube and SOGo (which is used by Mailcow, but hass fewer features than Roundcube) are the only somewhat modern looking options. All the other stuff looks like straight out of the 90s/early 2000s. Nextcloud Mail is pretty good as well.

I use RoundCube, I think it's one of the oldest solutions out there, and is pretty good (and not ugly as of a few years ago).

Other people already mentioned Roundcube and Snappymail, which are good options already.

There's also Cypht if you want a different approach. It combines multiple accounts into same interface so you can have a unified inbox.

In case you already have Nextcloud, there is an E-Mail client app for it.

I use roundcube.

The usual ones are RoundCube and SnappyMail (which is a fork of deprecated RainLoop). I’m hosting SnappyMail to access my Dovecot when no other mail client is handy.

@Charlxmagne @selfhosted I use Sogo along mailcow and it is the nicest I've seen.

To make it seamless so you can still Thunderbird, someone made a Docker image of it here: https://hub.docker.com/r/kebles/wanderbird But, you can probably find a newer release somewhere newer than 4 yrs old like this one. :) The point is, if you are wanting to keep it in the Thunderbird umbrella, then it's most likely been Dockerized.

I've Tried Cypht recently, but if you are using Gmail, it has a conflict there so it won't work out of the box without some extra work I think.

There's squirrelmail.

I liked zimbra the time I used it but it is rather heavyweight complete collaboration suite.

I used Squirrelmail briefly. It had a minor security bug which was easy to fix, but when I reported it to the devs, I couldn't convince them that it was actually a bug. I decided that they weren't paranoid enough to be working on that type of software, so I stopped using it.

Currently I'm not self-hosting email but am using mxroute.com which has a FOSS mail client that seems ok. I can't check right now what it is, but maybe later.

Fastmail's webmail is pretty good and they said something a while back about releasing it as FOSS but idk if that has happened.

Right now I mostly use Thunderbird rather than webmail. It sucks in many ways but I've had too much going on to pursue alternatives.

I think Google got it right early on when they realized that email clients should be backed by a serious search engine. The search features of a typical IMAP server aren't enough and the one in Thunderbird is crap. So I think this is an area where FOSS clients could use some work, if it hasn't already been done.