hMailServer is an open source e-mail server that can be used by any user type from internet service providers, governments, all the way to regular users.
Most users will be comfortable using it as it supports the most common e-mail protocols (IMAP, SMTP, and POP3) and you have the option to integrate it with many existing web mail systems easily. There is also a score-based spam protection feature that can additionally be attached to your virus scanner allowing you to scan all your incoming and outgoing email. The interface is a little dated but don't let that fool you as it provides many useful tools and features. One of which is the anti-virus tool that can delete entire e-mails if malware is detected. It will also notify the sender and recipient. hMailServer also includes the ability to block specific attachments that contain certain extensions like BAT, CMD, COM, EXE, and MSP.
hMailServer comes with a COM library that can be utilized for integration with your other software. With the COM library, you can write scripts and full applications that utilize the included hMailServer features.