it is by email.
Just wanted to share what happened to me, in case someone else is in the same situation. Probably doesn't apply to most people, but just in the interest of sharing: my PPR was sent to an immigration firm my company used for my work permit renewal an year ago, even though I submit the PR application by myself and never put any of their information in there.
CIC somehow still had that firm mailing address (including email) as my mailing address details and did not update to what I entered in my PR application (my mailing address).
Luckily, they were kind enough of getting in touch with me and forward me the PPR email, otherwise I wouldn't know it ! the lawyer said this wasn't the first time it happened, and since they still had my contact info they could get in touch with me, otherwise they would simply reply to CIC saying the mailing address is incorrect.
Not sure what one can do to prevent that though. I did receive a ghost email before the PPR, the ghost email came on my correct email account (which is linked to MyCiC) but the PPR was sent to this lawyer's email.