I'm pretty new to KDE. I noticed that dolphin has this very handy option in a file's context menu > share > send via email... (that I was really missing in Cinnamon/Nemo that I used before).
When I click, it opens the Delta Chat client. As standard email app thunderbird is configured.

I did not find the location how I can configure (GUI / CLI / config file) to specify the email app to be used here.

I'd appreciate any hint

peta wrote:As standard email app thunderbird is configured.

In KDE system settings/applications/standard applications?

j12i wrote:

peta wrote:As standard email app thunderbird is configured.

In KDE system settings/applications/standard applications?

Well, in the KDE settings there is thunderbird configured.

However, when I try to send a file from Dolphin via context menu > share > Send via Email... Dolphon does not open thunderbird, but another email client (it was Delta Chat, now I installed KMail for to have a look and it opens KMail ...) But as I'm used to thunderbird with many installed extensions, I'd like to keep it (for now).