hMail Server is not available for Linux but there are plenty of alternatives that runs on Linux with similar functionality. The best Linux alternative is mailcow: dockerized, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to hMail Server and 14 are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to hMail Server are Dovecot (Free, Open Source), iRedMail (Freemium, Open Source), Citadel (Free, Open Source) and Axigen (Paid).
Atmail allows you to choose between on-premises or cloud deployment. Features include email, contact, calendar, task, storage, synchronisation and provisioning. It's extensible through a RESTful API and allows easy rebranding and white-labelling.
Email gateway application (SMTP server) that makes it easy for senders to adopt the latest authentication specifications ( SPF and DKIM) to comply with changing ISP policies for accountable outbound email delivery. No over hype. It just delivers.