If I get the post code wrong but the rest of the address right, the letter will get through. If I make a typo in the name or address, the letter will get through.
If I make even the tiniest of typos in the email address, it'll fail.
I've written a totally wrong post code and city name before and still gotten a successful delivery. (Totally wrong as in, post code for my previous house in a different region, and the name of a neighbouring city instead of my city.) When I saw that I was really impressed with the postal service, and not quite as impressed by me. :)
I have no first hand information about overall rates, but there are dead letter offices, teams of people dedicated to finding the right destination for ill-addressed items, and I personally get snail-mail delivered to me, despite having errors in the address.
There is a resilience in snail-mail that has no equivalent in email.
