Microsoft Office Outlook Alternatives for Mac OS X

Thunderbird is a open source mail client developed and maintained by Mozilla foundation.

Apple Mail is an email client included with the operating systems macOS, iOS and watchOS by Apple Inc.

Postbox is powerful, intuitive, ultra-customizable, speedy task manager.

Calendar is a personal calendar application made by Apple Inc. that runs on both the macOS desktop operating system and iOS mobile operating system.

Airmail is a fast mail client for Mac and iPhone.

Sylpheed is an open-source e-mail client and news client licensed under the GPL.

Mutt is a text-based email client for Unix-like systems.

Zimbra Desktop is an offline client that lets you manage various email accounts in one desktop tool.

KMail is the email component of Kontact, the integrated personal information manager from KDE.

Open365 is an all-in-one productivity suite, based on KDE, Seafile, LibreOffice, Docker, and Jitsi.

Spark is a fast, smart mail manager app.

Polymail is an email application for OS X and iOS known for its clean interface and additional features atop the Gmail platform.

MailMate is an IMAP email client for macOS featuring extensive keyboard control, Markdown integrated email composition, advanced search conditions.

BusyCal is a calendar app for mac.