Safari mailto: "This website has been blocked from automatically composing an email."

Various third party JavaScript libraries will intercept clicks on a tags in order to prevent navigation briefly while sending data to a server. Typically, they programatically trigger navigation via window.location.replace.

The change in Safari pops the warning when mailto/tel links are triggered in this way.

There was an interaction, but that's usually been stopped with preventDefault, and Safari doesn't care.

If you're using a library that's causing this issue, contact the creator and see if they can update it to skip preventDefault on mailto/tel links.

What i did not mention initially was that we called the mailto from the JavaScript part of out page. We now again tried to solve the issue by changing to a HTML Tag based mailto (with to and subject) and it now somehow works without that dialouge. So i assume this issue solved for myself, but i am open to any hints explaining the reasons. Therefor by now i do not flag this answer as the solution.

Happened for users because we used window.open(...) to open that link in new window.

Replaced to window.location.href = ... just for Safari :facepalm:.