Twitter is rolling out email notifications letting users know when someone they follow retweets or favorites one of their tweets.

This could be a subtle, but major step in increasing user engagement with Twitter. Upon Twitter co-founder Jack Dorsey’s return to the company, he spoke at Columbia University about some of his goals for the company. He talked about the challenge of keeping users engaged with relevant incoming tweets, which can be a major element of making the product more useful to the user. Here’s what Dorsey had to say about that (as quoted by Peter Kafka):

We built very easy ways to input information. But extracting that information in a relevant way, in real time, is still a big, big challenge. So we need to build technologies that immediately surface what’s most revelant and most meaningful to you.

And that’s still a very, very large challenge, and difficult. You have to follow all of these accounts, and sometimes you miss some tweets that were extremly relevant to you. We can solve that through technology,  and we will solve that, but it is going to be quite difficult to do.

Twitter of course already has email notifications for when a user is sent a direct message, and when they’re followed by someone new, as well as updates from Twitter itself about new products, features, and tips and product or service updates related to users’ accounts.

The email notifications aren’t going to be the complete magical solution, but it is certainly a simple addition to Twitter that could end up going a long way in keeping users returning to Twitter. It works pretty well with Facebook. I know people that rarely go to Facebook at all, unless prompted by an email notification.

Both Twitter’s and Facebook’s use of email notifications highlight the fact that email is still a very important communication channel in the age of social media. You might even say that in some ways social media is largely dependent on email (don’t forget you need an email address to sign up for an account too).

As Twitter said, the feature is rolling out, so there’s a chance you don’t have it yet, but presumably you will soon.