Do SSPX Masses fulfill your Sunday obligation?

For the past few months I have been attending an SSPX mass in my city. Semi-regularly.

The Mass, of course, is beautiful. And Priest and  the people are very friendly. To my surprise,

But all of that really doesn't matter if I'm not fulfilling my Sunday obligation to attend Mass.

If assisting at an SSPX mass doesn't fulfill the Sunday obligation to attend mass, then a person is objectively in mortal sin, if they dont attend a regular mass as well.

So I ask the question:

Does attending a mass of the SSPX fulfill the Sunday obligation?