Best Open Source Email Software 2025 (original) (raw)
Browse free open source Email software and projects below. Use the toggles on the left to filter open source Email software by OS, license, language, programming language, and project status.
Passwordless Authentication and Passwordless Security
Identity is everything. Protect it with Duo.
It’s no secret — passwords can be a real headache, both for the people who use them and the people who manage them. Over time, we’ve created hundreds of passwords, it’s easy to lose track of them and they’re easily compromised. Fortunately, passwordless authentication is becoming a feasible reality for many businesses. Duo can help you get there.
Our Free Plans just got better! | Auth0 by Okta
With up to 25k MAUs and unlimited Okta connections, our Free Plan lets you focus on what you do best—building great apps.
You asked, we delivered! Auth0 is excited to expand our Free and Paid plans to include more options so you can focus on building, deploying, and scaling applications without having to worry about your security. Auth0 now, thank yourself later.- 1
• Designed for Linux and Windows email system administrators, Scrollout F1 is an easy to use, already adjusted email firewall (gateway) offering free anti-spam and anti-virus protection aiming to secure existing email servers, old or new, such as Microsoft Exchange, Lotus Domino, Postfix, Exim, Sendmail, Qmail and others. • Built-in multilayer security levels make configuration effort equal to a car radio. • It combines simplicity with effective protection using powerful open source with additional set of rules & filters. • Available as 64bit: - ISO image (Internet connection required during installation) - install from scratch (Internet connection required during installation). • Minimum Requirements (for 5,000 messages/day): 1 GB of RAM 30 GB storage drive 1 Processor x86/AMD64 1 Ethernet x 1 IPv4 address UDP ports: 53 123 4500 6277 24441 TCP ports: 25 80 443 2703
Downloads: 127,329 This Week
Last Update: 2018-04-08
See Project - 2
The Anti-Spam SMTP Proxy (ASSP) Server project aims to create an open source platform-independent SMTP Proxy server which implements auto-whitelists, self learning Hidden-Markov-Model and/or Bayesian, Greylisting, DNSBL, DNSWL, URIBL, SPF, SRS, Backscatter, Virus scanning, attachment blocking, Senderbase and multiple other filter methods. Click 'Files' to download the professional version 2.8.1 build 24261. A linux(ubuntu 20.04 LTS) and a freeBSD 12.2 based ready to run OVA of ASSP V2 are also available for download. NOTICE: V1 development has been stopped at the end of 2014 (1.10.1 build 16060). Possibly there will be done some bugfixing in future. Please upgrade to V2, which is and will be actively maintained.
Downloads: 49,420 This Week
Last Update: 2025-04-08
See Project - 3
Please install the latest version >4.0, because it uses the new Google People API. The Google Contacts API is now deprecated and is scheduled for sunset on June 15, 2021. GO Contact Sync Mod synchronizes your Microsoft Outlook contacts with your Google Mail address book, including pictures, categories and contact notes. It also syncs your Outlook Calendar Appointments on demand to Google Calendar. This Mod fork adds many enhancements and bug fixes to the obviously dead project 'Go Contact Sync'. Minimum requirement for GO Contact Sync Mod is .NET 4.7.2 and Windows 7 (32 or 64 bit).
Downloads: 2,378 This Week
Last Update: 2025-04-14
See Project - 4
Free Windows Mbox Viewer. Gain access to mbox archives or single eml messages. View attachments and export single mails in eml format. Access large mbox files such as Google Takeout or Mozilla Thunderbird Archives. Development of mbox viewer continues now at github: https://github.com/eneam/mboxviewer **NOTE**: Windows Defender may sometimes report incorrectly that mbox-viewer contains malware. Please report the case to the development. Development will ask Windows Security to update Windows Defender rules to resolve the issue. Last time the incorrect detection was corrected by Microsoft Security within few hours. User will need to run Windows Update to install the latest updated detection rules.
Downloads: 1,494 This Week
Last Update: 2 days ago
See Project
Comprehensive Cybersecurity to Safeguard Your Organization | SOCRadar
See what hackers already know about your organization – and stop them from getting in.
Protect your organization from cyber threats with SOCRadar’s cutting-edge threat intelligence. Gain 360° visibility into your digital assets, monitor the dark web, and stay ahead of hackers with real-time insights. Start for free and transform your cybersecurity today.- 5
milter manager
Protects you from spam mails and virus mails effectively with milter
This project has been moved to https://milter-manager.osdn.jp/ milter manager protects you from spam mails and virus mails effectively with milter. milter manager has embedded Ruby interpreter to control milters flexibly. milter manager can be used with Sendmail on Postfix on Ubuntu, CentOS, FreeBSD and so on.
Downloads: 3,162 This Week
Last Update: 2016-11-17
See Project - 6
Free Outlook Plugin, which synchronizes events, tasks and contacts between Outlook and Google, SOGo, NextCloud, Horde or any other CalDAV or CardDAV server. Supported Outlook versions are 2021, 2019, 2016, 2013, 2010 and 2007 and Office 365 for Desktop. This project was initially developed as a master thesis project at the University of Applied Sciences Technikum Wien, Software Engineering Degree program. Outlook CalDav Synchronizer is Free and Open-Source Software (FOSS), still you can support the project by donating on Sourceforge or directly within the About dialog of our Plugin. Contact us for enterprise support at https://caldavsynchronizer.org/enterprise/contact
Downloads: 902 This Week
Last Update: 2024-12-26
See Project - 7
Ever wanted to get rid of Outlook ? DavMail is a POP/IMAP/SMTP/Caldav/Carddav/LDAP gateway allowing users to use any mail client with Exchange and Office 365, even from the internet through Outlook Web Access on any platform, tested on MacOSX, Linux and Windows
Downloads: 762 This Week
Last Update: 2025-04-16
See Project - 8
PHPMailer
The classic email sending library for PHP
PHPMailer – A full-featured email creation and transfer class for PHP. Support for UTF-8 content and 8bit, base64, binary, and quoted-printable encodings. SMTP authentication with LOGIN, PLAIN, CRAM-MD5, and XOAUTH2 mechanisms over SMTPS and SMTP+STARTTLS transports. Validates email addresses automatically. Many PHP developers need to send email from their code. The only PHP function that supports this directly is mail(). However, it does not provide any assistance for making use of popular features such as encryption, authentication, HTML messages, and attachments. Formatting email correctly is surprisingly difficult. There are myriad overlapping (and conflicting) standards, requiring tight adherence to horribly complicated formatting and encoding rules – the vast majority of code that you'll find online that uses the mail() function directly is just plain wrong, if not unsafe!
Downloads: 173 This Week
Last Update: 2024-11-24
See Project - 9
MailHog
Web and API based SMTP testing
Inspired by MailCatcher, easier to install. Built with Go, MailHog runs without installation on multiple platforms. Run it from Docker Hub or using the provided Dockerfile. The SMTP server starts on port 1025, the HTTP server starts on port 8025, in-memory message storage. ESMTP server implementing RFC5321. Support for SMTP AUTH (RFC4954) and PIPELINING (RFC2920). Web interface to view messages (plain text, HTML or source). Supports RFC2047 encoded headers. Real-time updates using EventSource. Release messages to real SMTP servers. Chaos Monkey for failure testing. HTTP API to list, retrieve and delete messages. See APIv1 and APIv2 documentation for more information. HTTP basic authentication for MailHog UI and API. Multipart MIME support. Download individual MIME parts. In-memory message storage. MongoDB and file based storage for message persistence. Lightweight and portable. No installation required.
Downloads: 111 This Week
Last Update: 2021-07-09
See Project
Turn Your Content into Interactive Magic - For Free
From Canva to Slides, Desmos to YouTube, Lumio works with the tech tools you are already using.
Transform anything you share into an engaging digital experience - for free. Instantly convert your PDFs, slides, and files into dynamic, interactive sessions with built-in collaboration tools, activities, and real-time assessment. From teaching to training to team building, make every presentation unforgettable. Used by millions for education, business, and professional development.- 10
Blat - A Windows (32 & 64 bit) command line SMTP mailer. Use it to automatically eMail logs, the contents of a html FORM, or whatever else you need to send.
Downloads: 432 This Week
Last Update: 2022-08-01
See Project - 11
SquirrelMail is a PHP-based Web email client. It includes built-in pure PHP support for IMAP and SMTP, and renders all pages in pure HTML 4.0 for maximum compatibility across browsers. It has strong MIME support and a flexible plugin system.
Downloads: 371 This Week
Last Update: 1 day ago
See Project - 12
The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, Webmail, calendaring, and mailing list services.
Downloads: 331 This Week
Last Update: 6 days ago
See Project - 13
E-MailRelay is a simple SMTP proxy and relay MTA, written in C++, for Linux and Windows. As a proxy all messages can be passed through a user-defined program, such as a spam-filter, which can drop, readdress, or edit messages as they pass through.
Downloads: 293 This Week
Last Update: 2025-03-29
See Project - 14
Elastix
Unified Communications Server
Elastix is a software-based PBX powered by 3CX and based on Debian. An open-standards solution, Elastix is an easy to install and manage UC system compatible with popular IP phones, gateways and SIP trunks. Elastix is complete with unified communications features such as integrated WebRTC video conferencing, chat, presence and softphones and smartphone clients for Windows, Mac, iOS and Android.
Downloads: 243 This Week
Last Update: 2021-11-04
See Project - 15
theHarvester is a very simple to use, yet powerful and effective tool designed to be used in the early stages of a penetration test or red team engagement. Use it for open source intelligence (OSINT) gathering to help determine a company's external threat landscape on the internet. The tool gathers emails, names, subdomains, IPs and URLs using multiple public data sources.
Downloads: 53 This Week
Last Update: 2025-04-13
See Project - 16
trixbox CE is an easy to install, VOIP phone system based on the Asterisk PBX. trixbox is designed for home or office use. trixbox CE includes CentOS linux, mysql, and all the tools needed to run a business quality phone system. (formerly asterisk@home)
Downloads: 186 This Week
Last Update: 2013-06-18
See Project - 17
PHPMailer
A full-featured email creation and transfer class for PHP
A PHP email creation and transport class featuring file attachments, SMTP servers, CCs, BCCs, HTML messages, word wrap, and more. Sends email via sendmail, PHP mail(), QMail, or with SMTP. PHPMailer is used by many popular PHP development frameworks and is one of the most popular email-generating and sending libraries in the world. This project is defunct here on sourceforge – it's now maintained on Github at https://github.com/PHPMailer/PHPMailer. Documentation is available at https://github.com/PHPMailer/PHPMailer/wiki
Downloads: 178 This Week
Last Update: 2024-11-25
See Project - 18
Outlook Mail Merge Attachment is a script which can be used to add an attachment to an mail merge in Microsoft Outlook.
Downloads: 220 This Week
Last Update: 2014-05-02
See Project - 19
MsgViewer is email-viewer utility for .msg e-mail messages, implemented in pure Java. MsgViewer works on Windows/Linux/Mac Platforms. Also provides a java api to read mail messges (msg files) programmatically.
Downloads: 199 This Week
Last Update: 2016-05-01
See Project - 20
Open source DKIM library, MTA filter implementation and associated tools.
Downloads: 165 This Week
Last Update: 2022-07-25
See Project - 21
phpList
Powerful Open Source Email Marketing app with analytics & segmentation
phpList delivers Open Source email marketing, including analytics, list segmentation, content personalisaton and bounce processing. Extensive technical features and a secure and stable codebase are the result of over 17 years of continuous development. Used in 95 countries, available in 20+ languages, and used to send 25 billion email campaigns last year. Deploy it with your own SMTP server, or get a free hosted account at http://phplist.com.
Downloads: 164 This Week
Last Update: 2025-01-15
See Project - 22
The bogofilter package implements a fast Bayesian spam filter as suggested by Paul Graham in "A Plan For Spam" http://www.paulgraham.com/spam.html. It is written in C. Supported platforms: Linux, FreeBSD, Solaris, OS X, HP-UX, AIX, RISC-OS, ...
Downloads: 228 This Week
Last Update: 20 hours ago
See Project - 23
PostfixAdmin is a Web Based Management tool created for Postfix. It is a PHP based application that handles Postfix Style Virtual Domains and Users that are stored in MySQL, PostgreSQL or SQLite
Downloads: 106 This Week
Last Update: 2024-12-20
See Project - 24
Mailspring
A faster, leaner email client and fork of Nylas Mail
Mailspring is a fast and lean mail client that’s a new version of Nylas Mail. It’s maintained by one of Nylas Mail’s original authors, with plenty of great features and enhancements such as a new C++ sync engine that allows it to use 50% less RAM. Heavy dependencies have also been removed and the package manager rewritten for even greater speed. Written in TypeScript with Electron and React, it is cross-platform (macOS, Windows and Linux) and designed to be easy to extend.
Downloads: 22 This Week
Last Update: 2025-01-27
See Project - 25
Tutanota
Open source email service with a strong focus on security and privacy
Tutanota is an open source email client focused on security and privacy. It is built with end-to-end encryption and 2FA, so you can be assured of utmost email security. Tutanota is always encrypted, so whether you’re using their secure webmail client, mobile apps or desktop clients, you can be sure to communicate securely.
Downloads: 13 This Week
Last Update: 2025-04-14
See Project