Thunderbird ist nicht anderen Mailclients unterlegen, sondern dem Wechsel der Nutzer hin zu zentralisierten Webmail-Services. Die Idee hinter Thunderbird (Dezentralisierung, Sicherheit, Datenschutz) unterlag damit auch der Bequemlichkeit bunter Webmail-Oberflächen.
Thunderbird started strong as a second-mover with tens of millions of users. But, as technology and consumers moved to web solutions — relying on heavy servers and light clients that provided rich and instant access to email from anywhere — desktop clients became less and less relevant. Mozilla is culturally distrustful of any product that centralizes user data, so it invested in desktop-centric, server-agnostic solutions. […] Mozilla’s email presence atrophied […] the company quietly lost the war, letting the future of communication fall into the control of companies that are ultimately beholden to their bottom line, and not the user’s best interest.
Oder anders: IMAP vor Datenschutz.