Most of the spam I get in gmail apparently comes from other gmail accounts. Presumably google already filtered out senders pretending to be gmail, so I am not sure what a big improvement this will be for the average user.
Are they actually from Gmail accounts, or are they simply spoofing the sender? My bet is on the latter, because Google has heavy restrictions on Gmail that make it impractical to use for sending bulk spam.
> I am not sure what a big improvement this will be for the average user.
It's not going to be particularly noticeable for the average user, except for the second part (single-click unsubscribe, as opposed to a multi-step flow, is slightly stricter than what's required by CAN-SPAM). It will probably make Google's work easier, though, by having a publicly-known policy of rejecting emails without DKIM, as opposed the the status quo of having that be merely an open secret.