- https://elliot.land/validating-an-email-address 
- Cyrus IMAP - Cyrus IMAP is an email, contacts and calendar server. Cyrus is free and open source.
- OfflineIMAP - a GPLv2 software to dispose your mailbox(es) as a local Maildir(s). For example, this allows reading the mails while offline without the need for your mail reader (MUA) to support disconnected operations. OfflineIMAP will synchronize both sides via IMAP.
- imapfw - started to become the next generation OfflineIMAP with a new approach and extended features.
- Official imapsync migration tool ( release 1.836 ) - Imapsync is an IMAP transfers tool. The purpose of imapsync is to migrate IMAP accounts or to backup IMAP accounts. IMAP is one of the three current standard protocols to access mailboxes, the two other are POP3 and HTTP with webmails, webmails are often tied to an IMAP server.
- https://github.com/RaymiiOrg/NoPriv - NoPriv.py is a python script to backup any IMAP capable email account to a HTML archive, nicely browsable, instead of weird folders (Maildir), one huge file (mbox), only needing a web browser to view (thunderbird) and no propritary code, so you can make sure I don't steal your password.
- Sending files as mail attachments
- Ask HN: How do you do your email delivery?
- https://en.wikipedia.org/wiki/mbox - a generic term for a family of related file formats used for holding collections of email messages, first implemented for Fifth Edition Unix.
- mboxgrep - displays email messages matching a pattern
- https://en.wikipedia.org/wiki/Maildir - a common way of storing e-mail messages, where each message is kept in a separate file with a unique name, and each folder is a directory. The local filesystem handles file locking as messages are added, moved and deleted. A major design goal of Maildir is to eliminate program code having to handle locking, which is often difficult.
- DavMail - a POP/IMAP/SMTP/Caldav/Carddav/LDAP exchange gateway allowing users to use any mail/calendar client (e.g. Thunderbird with Lightning or Apple iCal) with an Exchange server, even from the internet or behind a firewall through Outlook Web Access. DavMail now includes an LDAP gateway to Exchange global address book and user personal contacts to allow recipient address completion in mail compose window and full calendar support with attendees free/busy display. 
- isync - a command line application which synchronizes mailboxes; currently Maildir and IMAP4 mailboxes are supported. New messages, message deletions and flag changes can be propagated both ways. isync is suitable for use in IMAP-disconnected mode.Synchronization is based on unique message identifiers (UIDs), so no identification conflicts can occur (as opposed to some other mail synchronizers).Synchronization state is kept in one local text file per mailbox pair; multiple replicas of a mailbox can be maintained.
- notmuch - a fast, global-search and tag-based email system to use within your text editor or in a terminal.
- SendEmail - a lightweight, command line SMTP email client. If you have the need to send email from a command line, this free program is perfect: simple to use and feature rich. It was designed to be used in bash scripts, batch files, Perl programs and web sites, but is quite adaptable and will likely meet your requirements. SendEmail is written in Perl and is unique in that it requires NO MODULES. It has an intuitive and flexible set of command-line options, making it very easy to learn and use.
- https://github.com/richfelker/mxclient - A minimalist client for sending mail direct to recipient's MX
list show commands
[number] select message r reply mail firstname.lastname@example.org send message
then type subject, then message, then ctrl-d (end of transmission)
- thunderbird - ARGH
- Evolution - a personal information management application that provides integrated mail, calendaring and address book functionality.
- Geary - an email application built around conversations, for the GNOME 3 desktop. It allows you to read, find and send email with a straightforward, modern interface.
- Claws Mail - an email client (and news reader), based on GTK+, featuring Quick response, Graceful, and sophisticated interface, Easy configuration, intuitive operation, Abundant features, Extensibility, Robustness and stability
- Sylpheed - lightweight and user-friendly e-mail client
- KMail - the email component of Kontact, the integrated personal information manager from KDE.
- sup - a console-based email client for people with a lot of email. It presents an interface of a list of threads, which are each hierarchical collections email messages. Threads can have multiple tags applied to them. It supports a very fast full-text search, automatic contact-list management, custom code insertion via a Ruby hook system, and more. If you’re the type of person who treats email as an extension of your long-term memory, Sup is for you.
- Alpine - a fast, easy to use email client that is suitable for both the inexperienced email user as well as for the most demanding of power users. Alpine is based on the Pine® Message System, which was also developed at the University of Washington. Alpine can be learned by exploration and the use of context-sensitive help. The user experience is highly customizable through the use of the Alpine Setup command.
- Trojitá - a fast Qt IMAP e-mail client
- Lumail - a modern console-based email client developed for GNU/Linux, supporting operations upon local Maildir hierarchies and remote IMAP mail-servers. The screenshots demonstrate what it looks like by default, and for a more interactive view you can watch this short ASCII-video.There are many graphical clients for email, but comparatively few designed solely for console use. With the exception of GNU Emacs none of the console clients I examined had any built in support for scripting with a real language.
- NeoMutt - a command line mail reader (or MUA). It's a fork of Mutt with added features.
- mu - a tool for dealing with e-mail messages stored in the Maildir-format, on Unix-like systems. mu’s main purpose is to help you to find the messages you need, quickly; in addition, it allows you to view messages, extract attachments, create new maildirs, ...
- notmuch - a fast, global-search and tag-based email system to use within your text editor or in a terminal...
- Mark J. Nelson: Search-oriented tools for Unix-style mail - A brief comparison of mu and notmuch
- Astroid Mail - a lightweight and fast Mail User Agent that provides a graphical interface to searching, display and composing email, organized in thread and tags. Astroid uses the notmuch backend for blazingly fast searches through tons of email. Astroid searches, displays and compose emails - and rely on other programs for fetching, syncing and sending email.
- aerc - a work in progress asynchronous email client for your terminal. aerc is network-first, and is designed with network-based email protocols in mind. It runs all network code in separate worker threads that don't lock up the UI. Compared to mutt, it's also easier on the network and much faster - it only fetches what it needs.
- Martin Lambers / msmtp · GitLab - an SMTP client. In the default mode, it transmits a mail to an SMTP server. To use this program with your mail user agent (MUA), create a configuration file with your mail account(s) and tell your MUA to call msmtp instead of /usr/sbin/sendmail.
- http://www.horde.org/apps/kronolith - calendar
- http://www.afterlogic.org/webmail-lite - Fast and easy-to-use webmail front-end for your existing IMAP mail server, Plesk or cPanel
openssl s_client -connect localhost.com:995
- https://github.com/emersion/maddy - Fast, cross-platform mail server
- https://github.com/emersion/hydroxide - A third-party, open-source ProtonMail CardDAV, IMAP and SMTP bridge
Stack and components
- Scrollout F1 is an easy to use, already adjusted email firewall (gateway) offering free anti-spam, anti-virus protection and Data Loss Prevention aiming to secure existing email servers, old or new, such as Microsoft Exchange, Lotus Domino, Postfix, Exim, Sendmail, Qmail and others.
- https://github.com/al3x/sovereign - A set of Ansible playbooks to build and maintain your own private cloud: email, calendar, contacts, file sync, IRC bouncer, VPN, and more.
- YunoHost - server operating system aiming to make self-hosting accessible to everyone. It is based on Debian GNU/Linux and is fully compatible with it. YunoHost automatically installs and configures some services around LDAP, and provides tools to administrate them.
- mailcow.email - The mailserver suite with the 'moo' – 🐮 + 🐋 = 💕
- https://github.com/vedetta-com/caesonia - OpenBSD Email Service
- https://gitlab.com/mailman/hyperkitty - an open source Django application under development. It aims to provide a web interface to access GNU Mailman v3 archives.
- Dada Mail - Make running your business and personal mailing lists easy, fun, and inexpensive.
- listmonk - Free and open source self-hosted newsletter and mailing list manager - 
- Autocrypt 1.0.0 documentation - a set of guidelines for developers to achieve convenient end-to-end-encryption of e-mails. It specifies how e-mail programs negotiate encryption capabilities using regular e-mails. For users, Autocrypt Level 1 offers single-click, opt-in encryption, eases encrypted group communications, and provides a way to setup encryption on multiple devices.
The Sender Policy Framework (SPF) is an open standard specifying a technical method to prevent sender address forgery. More precisely, the current version of SPF — called SPFv1 or SPF Classic — protects the envelope sender address, which is used for the delivery of messages. See the box on the right for a quick explanation of the different types of sender addresses in e-mails.
(There are other solutions that protect the header sender address or that do not care at all about who sent the message, only who originally wrote it.)
Even more precisely, SPFv1 allows the owner of a domain to specify their mail sending policy, e.g. which mail servers they use to send mail from their domain. The technology requires two sides to play together: (1) the domain owner publishes this information in an SPF record in the domain's DNS zone, and when someone else's mail server receives a message claiming to come from that domain, then (2) the receiving server can check whether the message complies with the domain's stated policy. If, e.g., the message comes from an unknown server, it can be considered a fake.
Once you are confident about the authenticity of the sender address, you can finally "take it for real" and attach reputation to it. While IP-address-based reputation systems like Spamhaus or SpamCop have prevailed so far, reputation will increasingly be based on domains and even individual e-mail addresses in the future, too. Furthermore, additional kinds of policies are planned for a future version of SPF, such as asserting that all of a domain's outgoing mail is S/MIME or PGP signed.
- DomainKeys Identified Mail (DKIM) lets an organization take responsibility for a message that is in transit. The organization is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for further handling, such as delivery. Technically DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic authentication.
- DMARC, which stands for "Domain-based Message Authentication, Reporting & Conformance", is a technical specification created by a group of organizations that want to help reduce the potential for email-based abuse by solving a couple of long-standing operational, deployment, and reporting issues related to email authentication protocols. DMARC standardizes how email receivers perform email authentication using the well-known SPF and DKIM mechanisms. This means that senders will experience consistent authentication results for their messages at AOL, Gmail, Hotmail, Yahoo! and any other email receiver implementing DMARC. We hope this will encourage senders to more broadly authenticate their outbound email which can make email a more reliable way to communicate.
- https://en.wikipedia.org/wiki/Joe_job - a spamming technique that sends out unsolicited e-mails using spoofed sender data. Early joe jobs aimed at tarnishing the reputation of the apparent sender or inducing the recipients to take action against them (see also e-mail spoofing), but they are now typically used by commercial spammers to conceal the true origin of their messages.
- Free JSON API to instantly check the spam score of your email messages - Have you ever wanted to process the spam score of incoming or outgoing email messages, but didn’t want the hassle of managing SpamAssassin? Now you can use our lightweight JSON API and instantly integrate spam score processing in your app. This service is provided for free from Postmark, the transactional email service for web apps.
- UCEPROTECT-Network - If you don’t like SPAM you can use our frequently updated GLOBAL BLACKLISTS free of charge, either private or commercial use.
- SpamCop.net - the premier service for reporting spam. SpamCop determines the origin of unwanted email and reports it to the relevant Internet service providers. By reporting spam, you have a positive impact on the problem. Reporting unsolicited email also helps feed spam filtering systems, including, but not limited to, SpamCop's own service.
- Spamhaus - an international nonprofit organization that tracks spam and related cyber threats such as phishing, malware and botnets, provides realtime actionable and highly accurate threat intelligence to the Internet's major networks, corporations and security vendors, and works with law enforcement agencies to identify and pursue spam and malware sources worldwide. As well as DNS-based Blocklists (DNSBLs) Spamhaus produces special data for use with Internet firewall and routing equipment, such as the Spamhaus DROP lists, Botnet C&C data, and the Spamhaus Response Policy Zone (RPZ) data for DNS resolvers which prevents millions of Internet users from clicking on malicious links in phishing and malware emails.
- MailScanner - highly respected open source email security system design for Linux-based email gateways. It is used at over 40,000 sites around the world, protecting top government departments, commercial corporations and educational institutions. This technology has fast become the standard email solution at many ISP sites for virus protection and spam filtering. MailScanner scans email for viruses, spam, phishing, malware, and other attacks against security vulnerabilities and plays a major part in the security of a network. By virtue of being open source, the technology in MailScanner has been reviewed many times over by some of the best and brightest in the field of computer security from around the world. MailScanner supports a wide range of MTAs and virus scanners to include the popular open source Clam AV. Spam detection is accomplished via Spamassassin, which is by far the most popular and standardized spam detection engine.
- MailWatch - A web based front-end to MailScanner
- https://github.com/vstakhov/rspamd - an advanced spam filtering system that allows evaluation of messages by a number of rules including regular expressions, statistical analysis and custom services such as URL black lists. Each message is analysed by Rspamd and given a spam score.
See Comms#PGP / GPG
Alliance including Lavabit n co.
- Autocrypt - a set of guidelines for developers to achieve convenient end-to-end-encryption of e-mails. It specifies how e-mail programs negotiate encryption capabilities using regular e-mails.For users, Autocrypt Level 1 offers single-click, opt-in encryption, eases encrypted group communications, and provides a way to setup encryption on multiple devices.
£3.30/user/month, or £33/user/year
"/opt/zimbra/zdesktop/linux/prism/zdclient" | -webapp "/home/milk/.zdesktop/data/zdesktop.webapp" | -override "/home/milk/.zdesktop/data/zdesktop.webapp/override.ini" | -profile "/home/milk/.zdesktop/data/profile"
- http://mandrill.com/ - from mailchimp
- https://github.com/sdushantha/tmpmail - a command line utility that allows you to create a temporary email address and receive emails to the temporary email address. It uses 1secmail's API to receive the emails.
- https://news.ycombinator.com/item?id=7386681 - zero inbox
- https://public-inbox.org/README.html - implements the sharing of an email inbox via git to complement or replace traditional mailing lists. Readers may read via NNTP, Atom feeds or HTML archives.
- https://github.com/ddevault/nanolist - a lightweight mailing list manager written in Go. It's easy to deploy, and easy to manage. It was written as an antithesis of the experience of setting up other mailing list software.