I led design for Outlook on iOS and Android while it grew from 100 million to more than 300 million weekly active users around the world. Here's what we did, and the one lesson I'd give any founder from it.
Email is the most used app nobody loves. People open it dozens of times a day, usually in a hurry, often on a train with one bar of signal. Outlook mobile was already big, but the job was clear: make it the fastest way to get through your inbox on a phone, for people at a Fortune 500 and people on the subway alike.
We treated every millisecond as a cost the user paid. Launch time, the time to see a new message, the time to triage a thread: each one got an owner and a number. A lot of the most important design work never showed up in a screenshot. It was deciding what to load first, and what to leave out.
We designed for how people actually use email on a phone: a few seconds at a time, one-handed, between other things. Swipe actions, a focused inbox, and fewer taps to the thing you came for mattered more than any new feature.
We built the team to work in the open and across time zones, sharing work early and often with engineering and with the people using it. I wrote about how that worked in Thoughts on building a successful remote team.
Growth at that scale didn't come from adding things. It came from removing friction, again and again, in the parts of the product people touch most. For an early-stage team the same rule applies with fewer users: find the moment people use your product most, measure how long it takes, and make it faster. It's the least glamorous roadmap there is, and it's the one that compounds.
If you're building something people use every day, here's what I look for, or send me your demo.