It's no secret that Instagram is starting to age and some users are turning away from the service in favor of other photo-sharing services. Instagram itself, however, is not ready to let its users go, and has introduced "Highlights" to be sent to users via email.

Highlights will begin being sent to users in the next few weeks, and will show users what it thinks are the best moments from people that they follow, essentially trying to rope older users back into using the social media network.

An Instagram spokesperson has confirmed that Highlights is the first time that Instagram has sent out any kind of promotional or re-engagement email. In fact, the feature is reportedly so new that if a user unsubscribes from the emails, they will not have a way to re-subscribe yet in their user settings.

The email is an attempt by Instagram to solve an issue that many aging social networks face - a drop in user engagement. This is especially problematic for a social media network that sorts posts chronologically or reverse-chronologically in the case of Instagram. Facebook, on the other hand, sorts posts in a user's feed by relevance, making it a little exciting and interesting for the individual user.

What essentially ends up happening for social media networks that sort chronologically is that there are so many posts in a feed that the interesting ones for a particular user are drowned out by those not as interesting. A feed gets so "noisy" that users tend to not be as engaged in posts, with engagement being one of Instagram's top priorities. It also leads to users being a little more careful in who they follow, which is another problem Instagram has when it wants users to be engaged with as many other users as possible.

Of course this problem can be avoided by offering users a way to see only content that they are interested in. Twitter is attempting to do the same thing with its new Discover page, which also happens to now be called Highlights. Facebook has also tested a number of ways to re-engage users, through both email and text messages. Most recently, some reports have said that Facebook is sending push notifications about engagements among their friends.

It will be interesting to see what kinds of tactics Instagram takes for re-engagement going forward. The company has "300 million" monthly active users; however, that number includes many people who rarely use the network. It certainly wouldn't be surprising to see the company introduce a "Highlights" section of its desktop site and its mobile app, allowing users to only see content that they want.