I've used Proton for a couple of years and have never had problems before today, so I think their engineering is of a high standard.

In fact, I applied for an Engineering Director role there not too long ago and they rejected me, so they must have extremely high standards!

I've been a Proton customer since before they started issuing proton.me email addresses. Never had any problems, including today. Right now I can check my email just fine.