I passed a cop doing 70 in a 55mph...?

and i was at a steady 70 too, i just didnt see the cop. My question is a friend told me that he caught my license plate and i would be getting a ticket in the mail? i have never heard of a speeding ticket through the mail, i would have thought if he was going to give me a ticket then he would just pull me over instead. Is it possible that i will recieve a ticket in the mail for 70 in a 55?! Another side note. everyone around me was ding the same speed. would he really give it to all those people as well?