GMail had a massive impact, but I didn't really think it was novel from a technical JS perspective. It was really basic, and loaded fast. It had excellent fast search and very good junk mail rejection.
Most email providers had approximately 100Mb mailbox limit (I can't remember specifically), but Gmail had 1Gb.
I remember Gmail invites. Ironically, Evan Williams (formerly of Twitter, now of Medium, at the time working at Google after they bought Blogger) was the person who sent me mine—and on the morning of April 1st, 2004. So I've had a Gmail account since the first day it was publicly available.
I actually got an invite from Google because I was on blogger.com back then (sad to admit it...)
I probably could have picked firstname@gmail.com were it not for the 6 letter minimum, so ended up with firstlast@gmail.com which still yields an absurd amount of messages meant to a variety of other recipients...
Most email providers had approximately 100Mb mailbox limit (I can't remember specifically), but Gmail had 1Gb.