Email is boring (but it works)
Long after Facebook, WhatsApp, Uber, and AirBnb are gone, email will still be there. It's the OG of the internet. It's a cornerstone of how we connect. Email has attempted to be fixed, changed or replaced. But, it's still there.
But despite it's cockroach-like nature, email is easy to forget about. But you shouldn't. Email is a relatively low-effort, automated and accessible way to help your users find their way back to your product. It's vital you can help users form habits in which your product makes up their day to day. Here's a few examples of how Monday.com, Xero, and Uber use email.
This is the initial email that gets sent after a user registers or signs on. Often there's a confirmation email that gets fired at the same time, or potentially, as a result of confirming the account.
You want to make it friendly, make it clear what they can do and what the next steps for the user is. Chances are the person signing up is already in the platform, so it's more of 'read later' or 'here's what you can do now' sort of vibe.
Following up, generally a day or two after the user has registered, is a great way to get the user to revisit your platform. Uber, in particular, is all about getting users to try it out. They realise for a (relatively) new service, getting a user to complete a trip increases the likelihood of using the service again. They rely on this so much that they give the first trip away for free.
Finally, the reminder or promotional email. This is something you want to do delicately. Don't spam. Always provide value in some way - even if it's not of monetary value, like a discount. For example, Xero, a tool for small businesses, don't offer cheaper subscriptions or deals - instead, they offer education and knowledge. Monday.com leverage your content and use it to tap you on the shoulder and say 'Hey, remember this?'. Uber offer regular discounts and excuses to open up the app. It's all about front of mind.
Next time your reviewing your retention, consider how email can play a part in getting users to come back. It's cheap, relatively easy to implement with third-party platforms, and very low-hanging fruit to reaching users outside your platform.