Nextcloud Mail is described as '💌 Mail app for Nextcloud' and is a Email Client in the office & productivity category. There are more than 25 alternatives to Nextcloud Mail for a variety of platforms, including Linux, Windows, Mac, BSD and Online / Web-based. The best alternative is Thunderbird, which is both free and Open Source. Other great apps like Nextcloud Mail are Microsoft Office Outlook, Mailbird, Evolution and Claws Mail.
KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.
Trojitá, is a fast Qt IMAP e-mail client that respects open standards and facilitates modern technologies. Trojitá values vendor-neutrality that IMAP provides and is committed to be as interoperable as possible.
LucaMail is an open source, cross-platform email client. LucaMail is developed to provide cross-platform alternative to Email Clients that are really exists. LucaMail focuses on modern technologies as well as maintaining a user-friendly UI.