They didn't need to; Hotmail offered free e-mail accounts which was unheard of at the time; Gmail went viral for offering 1GB of storage which was unheard of at the time. The latter also had scarcity with its invite system, I'm not sure if that helped make it more popular or not. Definitely helped prevent it from collapsing under its own success though.

Anyway, I think any service now that shows up offering something used by many that is now paid for free will become popular on its own.

Playing the lottery works too. Evidence: I see lottery winners. Therefore it must be a good business plan.

I'm too young to remember Hotmail launch but GMAIL did market. Their marketing investments were

1. Free Storage an order of magnitude larger that anything anyone provided at that time which was an unbeatable proposition. I'd say they ate the costs of storage as marketing investment.

2. Viral invitation format -> exclusively perception

I was quite young and things seemed shinier when I was young, so take this with a grain of salt. But I remember google differently. Gmail invites were a big deal, even amongst less technical people. Adding that sense of exclusivity to something they would use to advertise to us was remarkably smart.

Like another poster said, Hotmail offered free email accounts. Google offered 1GB of storage. Both of those things are "marketing".

In marketing there’s owned media, earned media, and paid media.

Google initially focused on the first two. They promoted new products like Gmail or Chrome on their search home page, and in the press. It worked well for them because they were already a newsworthy company with a lot of web traffic.

Today, they work quite hard at all three.

Hotmail did a fair amount of commercials https://youtu.be/IQRZcfAwn0g

Wasn't there a waiting list for Hotmail/Gmail in the beginning?