Earlier quoted context omitted.
Why?
Gmail and other really big providers are in a unique position for spam filtering. They have so many users that they get a continuously trained filter pretty much for free. They can instantly classify never-seen-before kind of spam in minutes because someone gets push notification on their phone and clicks "this is spam". Nobody with purely-technical solution to this problem can be better in practice. (although we're…
I am progressively transitioning to giving a unique email alias for each service.
1. If the address gets leaked or sold I can identify the culprit and stop the spam by deleting the alias
2. It is a useful security measure too, if a website gets hacked, it becomes harder to correlate my account across websites since it is a unique, non predictable address.