Thunderbird, Microsoft Office Outlook, Spark Mail, Mailbird, Apple Mail, Evolution, Mailspring, eM Client, EssentialPIM, Mutt, Geary, Mimestream, Juicy Mail, Microsoft Mail and Calendar, Trojitá, Kiwi for Gmail, Superhuman, Microsoft Outlook Express, WunderMail, ProfiMail, nPOPuk, Nylas Mail Lives, Unibox, Canary Mail, Inbox by Gmail, Nextcloud Mail, Mail Backup X, Calypso, Sylpheed, Zimbra Desktop, Mia for Gmail, SlideMail, Simple Mail, aerc, Claws Mail, Mailplane, Pantheon Mail, June.ai, Becky! Internet Mail, DreamMail, Ymail2, Clyton, Mynigma, FossaMail, GyazMail, MailTab for Gmail, Bluemail for mac, LeaderSend, Mailsmith, Spicebird, Mulberry, Mail Pilot, Mailburn, Smampi, MetroMail, MailBar are some alternatives to Postbox.