Thank you. I will send one that way from my main domain.
However, for the first time ever, I received bounced back and underliverable emails referencing the <email@example.com> email that is the default entry in the Spam Report Email section of the settings menu. This has never happened before, and also had the values in the private area which clearly reference the mailing service. I therefore believe that the actual messages arrived.
But I will send the last one using the method you suggested, just to be sure.