Well, might be a dumb question, but how do I send PMs/DMs here? Is there a restriction for new users? Like, having written a certain number of posts or something? I know things like that from other forums, but I can't find a hint on how it is handled here.

@TylerDurden told me to "click on a users name (or picon) to open the user profile and look for the envelope on the right." Well, the only envelope I see leeds me to my own (recieved) messages and when I click on "New Messages" (which leads to https://inkscape.org/alerts/message/) I get a "page not found" error. 

There seem to be missing some icons/pictures, too:

When I click on your username or avatar/picon, I get a profile and buttons on the right (see attached).

Nope, nothing there:

^^

EDIT: Ok, found the problem. Now it's working. :)

Note that the Inbox doesn't work for me.  I suspect it's a problem on Windows operating system, since the only people I know who can't use it are on Windows.  And those who can use it are on Linux.

Also note that you can still use PMs without the Inbox.  You just to make sure to get notified by email when someone sends you a PM.