Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Google Workspace - Google's encompassing suite of cloud-based business apps.
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Microsoft Exchange Server - Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.