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.
Roundcube Webmail is a browser-based, multilingual IMAP client with an application-like user interface. It provides the full functionality you expect from an email client, including MIME support, address book, and folder manipulation. High extensibility is granted by the plugin API and the user interface is fully skinnable using XHTML and CSS 2.
Mozilla Thunderbird is a total redesign of the Mozilla mail component to produce a cross-platform, stand-alone mail application using the XUL user interface language. It has many new features, among them the ability to customize your toolbars the way you want them. a new look and feel with a large number of downloadable themes which alter the appearance of the client, and the ability to add UI extensions.
KONSEC Kolab Server is a highly scalable, cluster-capable messaging and collaboration server that is based on the outstanding open source project, Kroupware. The KONSEC Konnektor is a simple client extension that gives Outlook complete group functionality through the Kolab Server, which employs the open standard IMAP together with ACLs, thus enabling you to collaborate in a unique mixed Windows/Linux environment.
NS WebMail offers standard mail functions for POP3 inbox management. Mail is sent using SMTP protocol. It has been designed to be light and simple, to avoid having to use heavy IMAP or SQL servers, and it has full MIME support for incoming and outgoing mail. It is Perl-strict and mod_perl-compliant, and has security using HTTP authentication or cookies. LDAP connectors are also available (as optional plug-ins) for authentication and read-only address book. Two interfaces are available (with and without frames). It is able to recognize tags from spam detection software (Spamassassin is supported out of the box).
Zimbra is a next-generation enterprise messaging and collaboration system. It features an Ajax Web client with conversation views, fast email search, Web service mash-ups, shared calendars, document authoring, and IM. The server also syncs to MS Outlook (via MAPI), the Apple desktop (via iSync, iCal, and CalDAV), POP/IMAP clients, and mobile devices (BlackBerry, smart phones, HTML Web browsers). A version of the Web client, Zimbra Desktop, also works offline with any POP/IMAP server. Administrators can control live backup/restores of individual or groups of mailboxes, hierarchical storage (HSM) and clustering, LDAP directory configuration, Web services integration with existing enterprise applications, and integrated anti-spam and anti-virus.
SendEmail is a lightweight, completely command line-based SMTP email delivery program. If you have the need to send email from a command prompt this tool is perfect. It was designed to be used in bash scripts, Perl programs, and Web sites, but it is also quite useful in many other contexts. It is written in Perl, and is unique in that it requires no special modules, and supports any platform that runs Perl. It has a straightforward interface, making it very easy to use.
This is a PHP class that attempts to validate a given e-mail address at three levels: matching the address against a RFC compliant regular expression, verifing the existence of the destination SMTP server by verifying the respective DNS MX record, and connecting to that server to see if the given address is accepted as a valid recipient. The class also features a debugging output option that lets you see the remote SMTP server connection and data exchange dialog to see the real cause why an apparently valid address may not be accepting messages.