To receive and deliver mails various types of mail servers are available following are some of them.
1)Sendmail:- Sendmail is the most popular Unix-based implementation of the Simple Mail Transfer Protocol (SMTP) for transmitting e-mail. When a sendmail server receives e-mail, it attempts to deliver the mail to the intended recipient immediately and, if the recipient is not present, it queues messages for later delivery. However, because it does not provide a mailbox facility and for other reasons, other software such as a POP3 or Internet Message Access Protocol server are also needed. Url:- http://www.sendmail.org/
2)Exim:- Exim provides great flexibility in the way mail can be routed, and there are extensive facilities for checking incoming mail. Exim can be installed in place of sendmail, although the configuration of exim is quite different to that of sendmail. http://www.exim.org/
3)Qmail:- Qmail is capable of handling millions of deliveries per day on a moderate system. Qmail writes mail to disk before it announces success. This way, even if there is a loss of power in the middle of a disk write, qmail will not lose mail. Url:- http://www.qmail.org/
4)pop3:- POP Post Office Protocol. This is used to describe how e-mail clients interact with mail servers. The POP3 Server is a type of mail server used for incoming mail. When users connect to their ISP POP servers, their e-mail software interface with the server and download any messages for them. POP is only used to receive messages, it is not used to send them.
5)SMTP:- SMTP is the protocol (or rules) by which email is delivered on the internet. Internet’s standard host-to-host mail transport protocol and traditionally operates over TCP, port 25. In other words, a UNIX user can type telnet hostname 25 and connect with an SMTP server, if one is present.
Url:- http://www.qksoft.com/qk-smtp-server/general-faq.html
6)courier-imap:-
built-in IMAP and POP3 aggregation proxy in Courier-IMAP. “Maildir” is a directory-based mail storage format. This is the same IMAP server that’s included in the Courier mail server, but configured as a standalone IMAP server that can be used with other mail servers - such as Qmail, Exim, or Postfix - that deliver to maildirs. Url:- http://www.courier-mta.org/imap/
7) Courier:-
Courier implements SMTP extensions for mailing list management and spam filtering. Courier can function as an intermediate mail relay, relaying mail between an internal LAN and the Internet, or perform final delivery to mailboxes. Courier uses maildirs as its native mail storage format, but it can also deliver mail to legacy mailbox files as well. Courier’s configuration is set by plain text files and Perl scripts. Most of Courier’s configuration can now be adjusted from a web browser, using Courier’s web-based administration module. Url:-http://www.courier-mta.org/
8)postfix:-
Postfix attempts to be fast, easy to administer, and secure, while at the same time being sendmail compatible enough to not upset existing users. Thus, the outside has a sendmail-ish flavor, but the inside is completely different.
Url:- http://www.postfix.org/
9)winmail server:-
Winmail Server is an enterprise class mail server software system offering a robust feature set, including extensive security measures. Winmail Server supports SMTP, POP3, IMAP, Webmail, LDAP, multiple domains, SMTP authentication, spam protection, anti-virus protection, SSL/TLS security, RBL ,SPF, SpamAssassin, Network Storage, remote access, Web-based administration, and a wide array of standard email options such as filtering, signatures, real-time monitoring, archiving, and public email folders. http://www.magicwinmail.net/
10)Merak mail server:-
Merak Email Server is a reliable, easy to use and afforable communication solution that is used by more than 30 million users worldwide. This powerful server solution contains every feature, module and extension you might desire and yet is extremely easy to administer. Url:- http://www.merakmailserver.com
11)kerio mail server:-
Kerio MailServer is a messaging and collaboration server that provides powerful protection against viruses and spam, and delivers secure access to e-mail, contacts, tasks and calendars. Kerio MailServer is suited for the needs of small and medium sized companies. Url:- http://www.kerio.com/
Six types of access to email
The user has six full-scope means of receiving email.
1. POP3 and secure POP3
2. IMAP4 and secure IMAP4
3. WebMail - graphical web interface (optional SSL)
4. Microsoft® Outlook via MAPI with Kerio Outlook Connector
5. Microsoft Entourage through WebDAV
6. Wireless email using handheld devices such as BlackBerry, Treo™, and PocketPC
12)cyrus-imap:-
This document gives an overview of the Cyrus IMAP server. The Cyrus IMAP (Internet Message Access Protocol) server provides access to personal mail and system-wide bulletin boards through the IMAP protocol. The Cyrus IMAP server is a scalable enterprise mail system designed for use from small to large enterprise environments using standards-based technologies.
http://www.faqs.org/docs/Linux-HOWTO/Cyrus-IMAP.html