POPFile is an abandoned free, open-source, cross-platform mail filter originally written in Perl by John Graham-Cumming and maintained by a team of volunteers. It uses a naive Bayes classifier to filter mail. This allows the filter to "learn" and classify mail according to the user's preferences. Typically it is used to filter spam mail. It can also be used to sort mail into other user defined "buckets" or categories - for example, the user may define a bucket into which work email is sorted.
The program works in several different modes. In the most popular mode, it sets itself up as a proxy between the email client and the POP3 server. As mail is downloaded via POP3, the filter identifies and classifies mail and makes a user defined modification to the subject line, appending the name of the appropriate bucket. The user then sets up rules in the mail client to sort the mail based on the subject line modification. An HTML based interface can be used to instruct POPFile, allowing users to correct errors in classifications and thus train the system to be sensitive to the user's specific requirements.
As an alternative to the subject-line modification (or as a supplement to it), the system can also be configured to use custom mail headers instead.
In another possible mode, POPFile can work as an IMAP client that monitors an IMAP server for incoming mail and also for messages moved by the user. Incoming emails are categorized and then immediately moved to the folder corresponding to the categorization. To train POPFile in this mode, the user only needs to move the message to the correct folder, i.e. to the folder where POPFile should have moved the message.
In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by RFC 9051.
In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common protocols for email retrieval.
An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email.
Mbox is a generic term for a family of related file formats used for holding collections of email messages. It was first implemented in Fifth Edition Unix.
Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft Office and Microsoft 365 software suites. Though primarily an email client, Outlook also includes such functions as calendaring, task managing, contact managing, note-taking, journal logging and web browsing, and has also become a popular email client for many businesses.
Apache SpamAssassin is a computer program used for e-mail spam filtering. It uses a variety of spam-detection techniques, including DNS and fuzzy checksum techniques, Bayesian filtering, external programs, blacklists and online databases. It is released under the Apache License 2.0 and is a part of the Apache Foundation since 2004.
Apple Mail is an email client included by Apple Inc. with its operating systems macOS, iOS, iPadOS and watchOS. Apple Mail grew out of NeXTMail, which was originally developed by NeXT as part of its NeXTSTEP operating system, after Apple's acquisition of NeXT in 1997.
The Bat! is an email client for the Microsoft Windows operating system, developed by Ritlabs, SRL, a company based in Chişinău, Moldova. There are two versions: a Home version and a Professional version. The Professional version includes a portable module, The Bat Voyager.
Pegasus Mail is a proprietary email client developed by David Harris. It was originally released in 1990 for internal and external mail on NetWare networks with MS-DOS and later Apple Macintosh clients. It was subsequently ported to Microsoft Windows, which is now the only platform actively supported. Previously freeware, Pegasus Mail is now donationware.
Email filtering is the processing of email to organize it according to specified criteria. The term can apply to the intervention of human intelligence, but most often refers to the automatic processing of messages at an SMTP server, possibly applying anti-spam techniques. Filtering can be applied to incoming emails as well as to outgoing ones.
Kontact is a personal information manager and groupware software suite developed by KDE. It supports calendars, contacts, notes, to-do lists, news, and email. It offers a number of inter-changeable graphical UIs all built on top of a common core.
The following tables compare general and technical features of notable email client programs.
The UW IMAP server was the reference server implementation of the Internet Message Access Protocol. It was developed at the University of Washington by Mark Crispin and others.
A mailbox is the destination to which electronic mail messages are delivered. It is the equivalent of a letter box in the postal system.
The Gmail interface makes Gmail unique amongst webmail systems for several reasons. Most evident to users are its search-oriented features and means of managing e-mail in a "conversation view" that is similar to an Internet forum.
An e-mail agent is a program that is part of the e-mail infrastructure, from composition by sender, to transfer across the network, to viewing by recipient. The best-known are message user agents and message transfer agents, but finer divisions exist.
EmailTray is a lightweight email client for the Microsoft Windows operating system. EmailTray was developed by Internet Promotion Agency S.A., a software development d.
OfflineIMAP is IMAP synchronization utility software, capable of synchronizing mail on IMAP server with local Maildir folder or another server.
Mail is an email client developed by Microsoft and included in Windows Vista and later versions of Windows. It is available as the successor to Outlook Express, which was either included with, or released for Internet Explorer 3.0 and later versions of Internet Explorer.
Mailfence is an encrypted email service that offers OpenPGP based end-to-end encryption and digital signatures. It was launched in November 2013 by ContactOffice Group, which has been operating an online collaboration suite for universities and other organizations since 1999.
