Hi,
I am a single applicant. CEC, from visa exempt country, landed May 15, thus I think I am eligible to give some thoughts re your inquiry.
When I got my PPR, it clearly states that I only have to send in COPIES of my passport due to the visa exempt thing. CIC even specified which page of the passport they want to see.
Don't get me wrong. They requested only COPIES of your passport doesn't necessarily means that you can send the response back to them via email. IF your PPR specifies they want something "original" (e.g. photos) one must send in the package via mail. Luckily, they didn't ask for any originals re my case thus I just sent the whole package (passport copies, RPRF receipt copy, bio data form) back to them via email. Easy and quick.
Hope this helps.