Opera (and actually all kinds of singing) should be without strain. The exception is if you put the strain on purpose for artistic interpretation, although this should rarely be used (like a fine herb to a meal). This man gives a great way on how to relax your larynx, aka voice box, down and back. Give it a quick listen and you’ll learn an awful lot!
Remember that you always need to resonate in your mask, even if you are dropping your larynx!