[sebastian]

Thanks for not letting Thunderbird die. In my opinion it's still the best and most customizable opensource email client and there is just not a viable replacement.

Most of the open source email clients I have tested require you to run a local webserver and access the mail using a web browser with very limited features. All I want/need is a desktop app that can be customized to work similar to Gmail, pulls and deletes emails from remote SMTP/IMAP servers and allows me to create backups locally.

Thunderbird gives me that.

[Sniffnoy]

It's been quite a while since I used it, but I recall Kmail being quite customizable. Indeed I actually remember it as being more customizable and had kind of been meaning to switch back to it from Thunderbird (but haven't actually done so because switching mail clients is a pain).

[bigbugbag]

kmail is in terrible state and has been for while (can't even send text email by default for several weeks (months?). IINM a replacement is being developed and kmail is on life support until then.

-edit- found it, it's kube: https://kube.kde.org/

[tormeh]

>the best and most customizable

Everything I've seen in the software industry suggests that these two qualities are at odds. The more config parameters there are, the more bugs and crap there will be. Unless by "best" you mean "most configurable" in which case, sure.

These days I run away from customizability. I'm actively choosing the least customizable software I can find.

[lucideer]

I have not found this to be the case at all.

Do you have examples?

[busterarm]

I've found Mutt, Alpine, Sup and Notmuch all to be very good, depending on your needs.

[stevekemp]

I wrote my own too - https://lumail.org/ - a console-based client which is half written in Lua, and completely scriptable.

[Maarius]

https://www.postbox-inc.com/ is also a nice alternative (and mostly compatible to Thunderbird - at least when I migrated)

[wslh]

Have you tried Sylpheed [1]? Sadly not well known but very mature.

[1] https://sylpheed.sraoss.jp/en/

[bigbugbag]

Also Claws[1].

[1]: http://www.claws-mail.org/

[wazoox]

Claws-mail does, too :)

[wiz21c]

Using claws-mail since 3 years, works really well (but I'm connected to the internet at all times, dunno how it works when out of connection)

[bigbugbag]

Is thunderbird customizable ? How so ?

I've been looking for ways to prevent it from opening tabs all around as this change to tabbed UX was forced upon users and confuses most of the people I maintain TB for, even to this day years later.

[seorphates]

Is it customizable? That seems like a pretty strange question from someone that maintains it for a user base. Apart from "disabling" tabs what are you looking to customize? Having used TB since inception I might think a more apt question is "What can't you customize?".

I also don't think I understand your tab stance. You don't have to base your usage on tabs, do you? Personally, given the volume and types of mail I deal with, I was waiting for tabs for years. I just want the context menu option to "view message in conversation" to always exist. It dropped off a couple of builds ago and I can't seem to get it back. Usability of mail without this is decreased exponentially.