No default applications when opening attachments in Kmail

[ironfuse at posteo.com]

When I open an attachment in Kmail, there is no default application for any file type. I have to manually select the program every time, even if I check the box to remember the default.

I use Kmail on i3. I have KDE installed as well. This problem does not happen if I log in to KDE, only on i3.

Can anyone please suggest how to troubleshoot this?