I take my previous claim back. I said that most seem to get PPRs through MyCIC messages. As the posters above mention, there seem to be many cases where that's not the case. Direct emails also seem to as likely, if not more likely (I have no data as to which is the more obvious route), way of getting PPRs. My rather limited research on this forum led me to believe MyCIC is the more prevalent route. I may have been wrong. In an ideal world, IRCC would update all relevant MyCIC accounts with the PPR pdf. However, that clearly doesn't seem to be happening. Gist of it: ye be warned.
I have seen a few posters claiming they got "warning" emails re: "you did not submit PPR within 30 months so you have X days to respond" but I don't have the links right now. Nor can I vouch for such claims (even if I could pull up such posts). Like the other poster above said, it is highly unlikely that CIC's emails get sent to the spam folder, but not everyone uses Gmail or other modern/up-to-date email vendors that have smart spam sensors. Hence my general advice to all: look up your spam folders etc.
Best wishes to all.