atmail is described as 'Atmail allows you to choose between on-premises or cloud deployment' and is an app in the Office & Productivity category. There are more than 25 alternatives to atmail for a variety of platforms, including Online / Web-based, Windows, Linux, Self-Hosted solutions and Mac. The best alternative is Zoho. It's not free, so if you're looking for a free alternative, you could try Zimbra Collaboration Suite or Horde. Other great apps like atmail are Google Workspace (Paid), Microsoft 365 (Paid), hMail Server (Free, Open Source) and Kolab Community (Freemium, Open Source).
Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more. With the most innovative web application available today, Zimbra boosts the productivity of users on any desktop and dramatically reduces TCO compared to legacy platform vendors.
Horde Groupware is a free, enterprise ready, browser based collaboration suite. Users can manage and share calendars, contacts, tasks and notes with the standards compliant components from the Horde Project.
Nextcloud is the most deployed on-premises file share and collaboration platform. Access & collaborate across your devices. As fully on-premises solution, Nextcloud Hub provides the benefits of online collaboration without the compliance and security risks.
Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft. It is part of the Microsoft Servers line of server products and is widely used by enterprises using Microsoft infrastructure solutions.
Low cost, easy to use Email Server software for virtual, on-premise, or hosted deployments for companies that want control of their email. Integrated web-mail with doc sharing, Drop Box integration, client and server side encryption.