IVS Milter is a virus, spam, and content milter. It makes use of the antivirus package ClamAV, and can also seamlessly integrate SpamAssassin (either spamc or libspamc). IVS Milter is also plugin based and currently supports virus scanning, spam scanning, content-type matching, attachment type matching, and attachment filename matching.
NullLogic Groupware is a modular Web-based groupware and email system designed for contact management and event scheduling. Additional features include private messaging, public discussion forums, webmail, shared bookmarks, file sharing, call tracking, order processing, an XML-RPC API, and integrated POP3 and SMTP servers.
MailWebForm allows you to send an email message from a Web site. It processes an HTML form, composes the email, optionally by processing a template, and delivers it. MailWebForm features spam protection in which the recipient's address is not specified in the HTML form, but rather uses property files to get the mail destination. Flexibility and ease-of-use are MailWebform's design goals. MailWebForm accepts three levels of parameter input: a global property file, user property files, and HTML form input. The setup is easily done through a administration Web site.
Hotwayd is a POP3/SMTP to HTTPMail (WebDAV) gateway. HTTPMail is a somewhat undocumented WebDAV-based protocol used by a variety of mail servers including Hotmail, MSN, Lycos, and Spray. Hotwayd allows you to use any standard POP3/SMTP mail reader to send and receive mail via these servers, similar to the way that Outlook Express can access a hotmail account. It supports features such as folder selection to get folders other than the inbox and proxy server support (if you require a proxy to access the internet).
vpopmail (vchkpw) is a collection of programs and a library to automate the creation and maintenance of virtual domain email configurations for qmail installations using either a single UID/GID or any valid UID/GID in /etc/passwd with a home directory. Features are provided in the library for other applications which need to maintain virtual domain email accounts. It supports named or IP-based domains. It works with vqadmin, qmailadmin, vqregister, sqwebmail, and courier-imap. It supports MySQL, Sybase, Oracle, LDAP, and file-based (DJB constant database) authentication. It supports SMTP authentication combined with the qmail-smtp-auth patch. It supports user quotas and roaming users (SMTP relay after POP authentication).