iMail is described as 'Fast, safe, heavy mail solution. Web-client access, LAN or WAN self-hosted server, maintenance-free design. No Windows server and database server required, unlimited mail accounts, storage, attachment size, custom logo. Free for commercial use' and is a Mail Server in the online services category. There are more than 25 alternatives to iMail for a variety of platforms, including Linux, Web-based, Windows, Self-Hosted and Mac apps. The best iMail alternative is Google Workspace. It's not free, so if you're looking for a free alternative, you could try mailcow: dockerized or Kolab. Other great apps like iMail are Zentyal, Zimbra Collaboration Suite, SOGo and Kopano.