Historical clue formulations

• Communication system for almost two billion people — 2025-12-02
• Communication service launched in 2004 — 2023-03-14
• App with an envelope logo — 2022-09-21
• Service with nearly two billion users — 2021-04-18
• Its logo has a blue, red, orange, yellow and green "M" — 2020-11-29
• App with an envelope icon — 2020-02-02
• Service with more than 1.5 billion users — 2020-01-19
• Online service introduced in 2004 — 2019-12-20
• Service launched on April Fool's Day in 2004 — 2019-09-28
• Yahoo alternative — 2019-03-03
• Outlook alternative — 2018-11-25
• Service with more than a billion users — 2018-02-11
• Communication service since 2004 — 2017-04-28
• Alternative to AOL or Yahoo — 2017-02-27
• Tech service with over half a billion users — 2015-02-20
• Priority Inbox offerer — 2011-01-15
• AOL alternative — 2008-09-05
• Big name in Web-based correspondence — 2008-07-11