Alternatives to Microsoft Exchange Online in 2026

Docker Mailserver docker-mailserver

Production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.) running inside a container.

Complete system Production-ready You want a simple self-hosted mail server without a web admin panel.

★ 20k MIT Shell Active, pushed today

Mailcow-dockerized mailcow

mailcow: dockerized - 🐮 + 🐋 = 💕

Complete system Production-ready You want to host email for several domains yourself with a full admin interface.

★ 14k GPL-3.0 JavaScript Active, pushed yesterday

Roundcubemail roundcube

The Roundcube Webmail suite

Complete system Production-ready You run an IMAP server and need a dependable webmail front end.

★ 7.3k GPL-3.0 PHP Active, pushed 8 days ago

WebClients ProtonMail

Monorepo hosting the proton web clients

Complete system Production-ready You want to audit or contribute to Proton's client code; to use Proton, sign up for the hosted service.

★ 5.7k GPL-3.0 TypeScript Active, pushed today

Cypht cypht-org

Cypht: Lightweight Open Source webmail aggregator [PHP, JS]. Supports IMAP/SMTP, JMAP and EWS (Exchange Web Services)

Complete system Production-ready You want a lightweight self-hosted webmail that aggregates mailboxes from different providers.

★ 1.8k LGPL-2.1 PHP Active, pushed today

Nextcloud Mail nextcloud

💌 Mail app for Nextcloud

Integration Production-ready Your team works in Nextcloud and wants email in the same interface as files and calendar.

★ 1.1k AGPL-3.0 JavaScript Active, pushed today

MailFlow maathimself

A self-hosted, unified webmail client.

Complete system Usable You juggle several mail accounts and want one self-hosted web interface for them.

★ 628 AGPL-3.0 JavaScript Active, pushed today

KumoMTA KumoCorp

The first Open-Source high-performance MTA developed from the ground-up for high-volume email sending environments.

Complete system Production-ready You send millions of emails and want an open alternative to commercial MTAs such as PowerMTA.

★ 571 Apache-2.0 Rust Active, pushed 4 days ago

Webmail-lite-8 afterlogic

Open-source webmail script for existing IMAP server

Complete system Production-ready A host or small company wants a free webmail front end on its own IMAP server, maintained by a commercial vendor.

★ 363 AGPL-3.0 Shell Active, pushed 7 days ago

Mailez mailez-hq

Self-hosted mail server for your own domain: SMTP/IMAP/POP3, CardDAV/CalDAV, React webmail and admin console, one-command Docker Compose.

Complete system Experimental You want an all-in-one mail server with modern webmail and are prepared to test a very new project thoroughly first.

★ 294 AGPL-3.0 Go Active, pushed 20 days ago

OmniMail mibgb65-cloud

Self-hosted multi-domain webmail on Cloudflare Workers, D1, R2, Queues, Email Routing, and Resend.

Complete system Experimental An individual or small team on Cloudflare wants serverless webmail for several domains without running a mail server.

★ 271 MIT TypeScript Active, pushed 17 days ago

JMAP webmail root-fr

Modern JMAP webmail client built for Stalwart Mail Server. Privacy-focused, responsive, with real-time updates.

Complete system Usable You run Stalwart and want a modern webmail designed for it.

★ 236 MIT TypeScript Active, pushed 43 days ago

Gofer cristianadrielbraun

Self-hosted multi-account email client with support for JMAP/IMAP/SMTP, direct integration with Gmail and Outlook APIs. Also Contacts and Calendar. Built with Go, templ, and HTMX, SQLite for storage

Complete system Usable You want one self-hosted interface for personal mail across providers and can live with pre-1.0 changes.

★ 169 MIT Go Active, pushed today

LanQin Email LanQin996

自托管邮件系统，提供现代化 Webmail 与管理后台，支持多域名、外部 IMAP、邮箱共享、细粒度权限和简繁英三语言。

Complete system Experimental A Chinese-speaking organisation wants a single-container mail server with a modern admin interface.

★ 167 GPL-3.0 Go Active, pushed 3 days ago

Ad-Hoc-Email-Server o4oren

An ad-hoc disposable temporary mail server. Create and use ad hoc disposable mailboxes for testing or any other purpose.

Developer tool Usable You need many throwaway mailboxes for testing or for sign-ups you expect to attract spam.

★ 412 Apache-2.0 TypeScript Slowing, pushed 7 months ago

Rapid-Inbox wendaochangsheng

Self-hosted inbound email infrastructure with a high-performance C++ SMTP ingestion engine, local storage, and developer APIs.

Developer tool Experimental You need throwaway inboxes for testing sign-up and notification emails in automated tests.

★ 128 MIT Python Active, pushed 3 months ago

OpenMail chenyuwebwawa

A self-hosted, open-source mail server suite in a single Node.js process — full-stack email with SMTP / IMAP / POP3, a modern three-pane webmail, an admin dashboard, multi-tenancy, DKIM, anti-spam and 2FA. Zero native dependencies, one SQLite file, up and running in minutes.

Complete system Experimental You want to experiment with a single-process mail server on a test domain.

★ 116 MIT JavaScript Active, pushed 13 days ago

OpenInbox sums001

Free, unlimited business email on your own domains, running entirely in your free Cloudflare account.

Complete system Experimental A small business already on Cloudflare wants free mailboxes for several domains and can tolerate beta software on a spare domain first.

★ 105 MIT TypeScript Active, pushed yesterday

Magma lavabit

The magma server daemon, is an encrypted email system with support for SMTP, POP, IMAP, HTTP and MOLTEN,. Additional support for DMTP and DMAP is currently in active development.

Complete system Experimental You are researching encrypted mail protocols; it is not a practical choice for running a mail service.

★ 1.8k AGPL-3.0 C Quiet, pushed 2 years ago

Mailur naspeh

Lightweight webmail inspired by Gmail

Complete system Experimental Only if you want to revive a tag-based webmail; there are maintained alternatives.

★ 788 GPL-3.0 Python Quiet, pushed 4 years ago

WebMail Lite afterlogic

AfterLogic WebMail Lite PHP. Fast and easy-to-use webmail front-end for your existing IMAP mail server, Plesk or cPanel.

Complete system Experimental Do not adopt this repository; Afterlogic's maintained version is WebMail Lite 8.

★ 455 AGPL-3.0 PHP Quiet, pushed 7 years ago

Isotope Mail manusa

Isotope Mail Client

Complete system Experimental Only as a code reference; the author calls it very early stage.

★ 242 Apache-2.0 JavaScript Quiet, pushed 4 years ago

Gmail (Google Workspace) Google

Stay on top of your inbox and keep your business safer with the secure, smart and easy-to-use Gmail.

Complete system Production-ready A business wants reliable hosted email with strong spam filtering and works mostly in the browser.

90k readers a month Since 2004 Commercial

Proton Mail Proton AG

Proton Mail is the world’s largest secure email service with over 100 million users. Available on Web, iOS, Android, and desktop. Protected by Swiss privacy law.

Complete system Production-ready Privacy is your first concern and you want encrypted email, especially between Proton users.

12k readers a month Since 2014 Commercial

Fastmail Fastmail Pty Ltd

Fast, private email hosting for you or your business. More productive, lightning fast, simple and built to save you time.

Complete system Production-ready An individual, family or small business wants fast, private email on its own domain without Google or Microsoft.

586 readers a month Since 1999 Commercial

Zoho Mail Zoho Corporation

Ad-free Business Email Hosting with a clean, easy-to-use interface. Secure & professional with integrated business Calendar, Contacts, Notes & Tasks.

Complete system Production-ready A small business wants low-cost email on its own domain, particularly if it uses other Zoho apps.

Commercial