SmarterMail is the mail server software we use. Its made by SmarterTools who also makes SmarterStats, and SmarterTrack. WhiteSites has been using SmarterTools' products for over 10 years. One of the best features of SmarterMail is its free for companies with a single domain and up to 10 email accounts. This makes a very popular choice for startups. Then once your company out grows a single domain and or 10 email accounts you can buy a license that meets your needs. SmarterMail supports POP3, IMAP, and Exchange Server (requires upgraded license). It also features integration with RBLs (Realtime blacklists) which help reduce spam, and other advanced spam fighting features like greylisting.