MP3 Preview email does not arrive

This is not the first time.

When I preview my email, it shows beautifully in the window with the tabs for Desktop and Mobile. But when I send myself an email, it doesn’t arrive.

– Site Health -> Mail check does arrive
– I also send an email to a different domain (as this seemed to do the trick in an earlier similar situation)

Now what could be wrong?

Adventurous greetings, Coen.