getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
fdm (fetch and deliver mail) is a simple, lightweight replacement for mail fetching, filtering, and delivery programs such as fetchmail and procmail. It can fetch using POP3, POP3S, IMAP, IMAPS, or stdin, and deliver to a pipe, file, maildir, mbox, or SMTP server, based on a set of regexps. It can be used for both single user and multiuser setups, and is designed with privilege separation when running as root.
Kerio MailServer is an email and collaboration suite that comes integrated with direct over-the-air (OTA) ActiveSync support, over 14 anti-spam layers (including SpamAssassin), dual anti-virus options (including a ClamAV plugin), collaboration features in Outlook, Entourage, Outlook Mobile, VersaMail, WebMail, and iCal, email archiving, and live automated backups. It supports a variety of SSL-encrypted communication protocols including POP3, IMAP, STMP, and HTTP for WebDAV, CalDAV, Web mail, and wireless ActiveSync. Wireless capabilities include direct email push, synchronization of calendar events, contacts, and tasks, and remote wipe for Windows Mobile devices to delete company data in the event the device is lost or stolen. Authentication options include Active Directory, Apple Open Directory, PAM, and an internal database. It can be administered remotely using an encrypted channel.
Heirloom mailx (formerly known as "nail") is derived from Berkeley Mail and provides the functionality of the System V and POSIX mailx commands. Additional features include support for MIME, IMAP (including caching and disconnected use), POP3, SMTP, S/MIME, international character sets, maildir folders, message threading, powerful search methods, scoring, and a Bayesian junk mail filter. Mailx can be used as a mail batch language in nearly the same way as it is used interactively. It can thus act as a mailbox filter, can fetch mail from remote accounts, and can send files as attachments.
phPOP3clean is a spam, virus, and worm filtering system for POP3 email accounts. It is designed to run as a cron job and can catch spam based on links to blacklisted IPs, obfuscated words, or blacklisted phrases in the message body as well as attached-image spam, email worms, and corrupted or malformed emails.
The Gordano Messaging Suite (GMS) is a highly flexible and reliable suite of messaging products. Customers can choose which components meet their needs from email, Webmail, collaboration, instant messaging, calendaring, SMS, and list server software all of which can be complimented by high level anti-spam, anti-virus, and archiving options.
P3Scan is a full transparent proxy server for email clients. It runs on a Linux box with iptables (for port redirection). It can be used to provide email scanning from the Internet to any internal network, and is ideal for helping to protect your "Other OS" LAN from harm, especially when used in conjunction with a firewall and other Internet proxy servers. It is designed to enable scanning of incoming email messages for viruses, worms, trojans, spam, and harmful attachments. Because viewing HTML email can enable a spammer to validate an email address (via Web bugs), it can also provide HTML stripping.
MailStripper Pro is a mail scanner that aims to remove spam and viruses from incoming mail. It recognises and decodes many obfuscation techniques used by spammers and uses several different mechanisms to recognise spam which are immune to Bayes poisoning, and has achieved real-world success of over 99.8%. It is MTA-independent and does not implant itself into your mail server. Instead, it functions as a proxy, allowing the MTA to reside on a different server.
pop3spam is a POP3 client which connects to a POP3 server and deletes unsolicited mail. It's possible to check for messages that exceed a certain limit and to scan header lines for special patterns (regular expressions). If a message has been identified as unsolicited, it can be deleted directly from the POP3 server without the need to download it first. Eventually your normal mail-retrieval utility (e.g. fetchmail) can gather all (cleaned) mail as usual.