License & Deployment Mix: 17 tools – 9 OSS, 5 SaaS. (OSS and SaaS counts can overlap when an open-source tool also offers a vendor-hosted edition.)
What Is an Email Server Platform?
An email server platform is a complete solution for hosting and managing email accounts – sending, receiving, storing, and accessing messages via IMAP/POP3/SMTP. Unlike individual email components (an MTA like Postfix or an MDA like Dovecot), an email server platform bundles these components into an integrated product with user management, webmail, and administration tools.
This directory evaluates complete email server platforms, not individual email components (SMTP servers, MDAs, libraries).
Email Server vs Email Components
| Scope | Focus | Examples |
|---|---|---|
| Component | Single function (MTA, MDA, filter) | Postfix, Dovecot, Rspamd |
| Platform | Complete email hosting solution | Mailcow, Zimbra, Google Workspace |
A platform typically bundles:
- MTA (Mail Transfer Agent) – sends and receives email via SMTP
- MDA (Mail Delivery Agent) – delivers mail to user mailboxes, serves via IMAP/POP3
- Webmail – browser-based email client
- Admin UI – user and domain management
- Anti-spam / anti-virus – filtering pipeline
- Calendar / contacts – CalDAV/CardDAV (groupware features, varies by platform)
The information on these pages was researched by a combination of human review and large language models. To suggest an addition or correction, please contact us. Prepared by Rhodium Systems Inc., author of the ResorsIT platform — a unified IT operations management platform for IT teams and MSPs that integrates a curated suite of open-source, commercial, and SaaS applications into a single system with shared identity, single sign-on, access control, and a common audit trail. Use this catalogue only as a starting point for your own research, and review any tool carefully against your own requirements before relying on it. Catalogue data version 2026.197.
Comparison
Identity separation: email mailbox access (IMAP/POP3/SMTP) uses separate credentials from the primary web identity. SSO applies only to admin panels and webmail (browser-based access).
Protocol Support
| Tool | IMAP | POP3 | SMTP | JMAP | ActiveSync | CalDAV | CardDAV |
|---|---|---|---|---|---|---|---|
| Mailcow | Yes | Yes | Yes | No | SOGo | SOGo | SOGo |
| Mailu | Yes | Yes | Yes | No | No | No | No |
| docker-mailserver | Yes | Yes | Yes | No | No | No | No |
| iRedMail | Yes | Yes | Yes | No | SOGo | SOGo | SOGo |
| Modoboa | Yes | Yes | Yes | No | No | Radicale | Radicale |
| Stalwart | Yes | Yes | Yes | Yes | No | Yes | Yes |
| Maddy | Beta | No | Yes | No | No | No | No |
| Mail-in-a-Box | Yes | Yes | Yes | No | z-push | NC | NC |
| Zimbra | Yes | Yes | Yes | No | Yes* | Yes | Yes |
| Carbonio | Yes | Yes | Yes | No | CE* | Yes | Yes |
| Kerio Connect | Yes | Yes | Yes | No | Add-on | Yes | Yes |
| Axigen | Yes | Yes | Yes | No | Yes | Yes | Yes |
| Google Workspace | Yes | Yes | Yes | No | Yes | Yes | Yes |
| Microsoft 365 | Yes | Yes | Yes | No | Yes | No | No |
| Proton Mail | Bridge | No | Bridge | No | No | No | No |
| Fastmail | Yes | Yes | Yes | Yes | No | Yes | Yes |
| Zoho Mail | Yes | Yes | Yes | No | Yes | No | No |
* = requires commercial edition or paid add-on NC = via Nextcloud; SOGo = via bundled SOGo; Bridge = via Proton Mail Bridge desktop app
Best protocol support: Stalwart (native JMAP, IMAP4rev2, POP3, SMTP, CalDAV, CardDAV, WebDAV), Fastmail (JMAP co-author, IMAP, CalDAV, CardDAV)
Mobile Device & Groupware Sync
How each platform handles calendar, contacts, and mobile device synchronization.
| Tool | Calendar | Contacts | Mobile Sync |
|---|---|---|---|
| Mailcow | SOGo | SOGo | EAS (SOGo) |
| Mailu | No | No | IMAP only |
| docker-mailserver | No | No | IMAP only |
| iRedMail | SOGo | SOGo | EAS (SOGo) |
| Modoboa | Radicale | Radicale | CalDAV/CardDAV |
| Stalwart | Native | Native | CalDAV/CardDAV |
| Maddy | No | No | IMAP only |
| Mail-in-a-Box | Nextcloud | Nextcloud | EAS (Z-Push) |
| Zimbra | Native | Native | EAS* |
| Carbonio | Native | Native | EAS* |
| Kerio Connect | Native | Native | EAS (add-on) |
| Axigen | Native | Native | EAS |
| Google Workspace | Native | Native | EAS |
| Microsoft 365 | EAS only | EAS only | EAS |
| Proton Mail | No | No | App only |
| Fastmail | Native | Native | CalDAV/CardDAV |
| Zoho Mail | EAS only | EAS only | EAS |
* = commercial edition or paid tier required EAS = Exchange ActiveSync (single-account setup on both iOS and Android) CalDAV/CardDAV = iOS native; Android requires DAVx5 app EAS only = no CalDAV/CardDAV; calendar/contacts sync only via EAS or vendor app IMAP only = no calendar or contacts; add Radicale, SOGo, or Z-Push separately App only = requires vendor’s mobile app
iOS vs Android Experience
| Mobile Sync | iOS | Android |
|---|---|---|
| EAS | 1 account, native | 1 account, native |
| CalDAV/CardDAV | Native (2 accounts) | DAVx5 app required |
| IMAP only | Email only | Email only |
| App only | Vendor app | Vendor app |
Best mobile experience: Platforms with EAS (Mailcow, iRedMail, Mail-in-a-Box, Zimbra, Axigen, Google Workspace, Microsoft 365)
Good with iOS, needs DAVx5 on Android: Stalwart, Modoboa, Fastmail
Email only (no groupware): Mailu, docker-mailserver, Maddy – add Radicale or SOGo for CalDAV/CardDAV, optionally Z-Push for EAS
Admin Panel & Webmail SSO
SSO applies to browser-based access only (admin panel and webmail). Mailbox protocol access (IMAP/POP3/SMTP) always uses separate credentials.
| Tool | Admin OIDC | Admin SAML | Admin LDAP | Webmail SSO |
|---|---|---|---|---|
| Mailcow | Yes | No | Yes | OIDC (SOGo) |
| Mailu | Proxy* | Proxy* | No | Centralized |
| docker-mailserver | N/A | N/A | N/A | N/A |
| iRedMail | No | No | Backend | SOGo SAML |
| Modoboa | Yes | No | Yes | OIDC |
| Stalwart | Yes | No | Yes | N/A* |
| Maddy | N/A | N/A | N/A | N/A |
| Mail-in-a-Box | No | No | No | No |
| Zimbra | No | Yes | Yes | SAML |
| Carbonio | No | Yes* | Yes | SAML* |
| Kerio Connect | No | No | AD | No |
| Axigen | No | No | Yes | OIDC |
| Google Workspace | Yes | Yes | Sync | OIDC/SAML |
| Microsoft 365 | Yes | Yes | Sync | OIDC/SAML |
| Proton Mail | No | 2026* | No | No |
| Fastmail | 2026* | No | No | No |
| Zoho Mail | No | Yes | Sync | SAML |
* = community fork, commercial edition only, planned, or limited availability N/A = no admin panel or no webmail bundled Proxy = via reverse-proxy header authentication Sync = LDAP/AD directory sync (not login)
Best admin SSO: Mailcow (native OIDC + LDAP), Modoboa (OIDC + LDAP), Stalwart (OIDC + LDAP)
Identity Separation
How well does each platform support separate mailbox credentials independent of the primary identity (SSO)?
| Tool | Separate Mailbox Password | App Passwords | Risk |
|---|---|---|---|
| Mailcow | Yes | Yes (OIDC users) | None |
| Mailu | Yes | N/A | None |
| docker-mailserver | Yes | N/A | None |
| iRedMail | Yes | N/A | None |
| Modoboa | Yes | N/A | None |
| Stalwart | Yes | Yes | None |
| Maddy | Yes | N/A | None |
| Mail-in-a-Box | Shared* | No | Low |
| Zimbra | Yes | N/A | None |
| Carbonio | Yes | N/A | None |
| Kerio Connect | Depends* | No | Medium |
| Axigen | Yes | Yes | None |
| Google Workspace | App pwd* | Yes | Medium |
| Microsoft 365 | No* | Deprecated | High |
| Proton Mail | Yes (Bridge) | N/A | None |
| Fastmail | Yes | Yes (scoped) | None |
| Zoho Mail | Yes | Yes (with 2FA) | None |
Shared* = same password for webmail, IMAP, admin Depends* = separate with internal auth; shared when AD-mapped App pwd* = app passwords available but at risk of deprecation (OAuth-only trajectory) No* = basic auth deprecated 2022; app passwords being deprecated March–April 2026; OAuth-only mandatory
Best identity separation: All self-hosted OSS platforms (full control over credentials), Proton Mail (Bridge creates separate credentials), Fastmail (scoped app passwords)
Worst identity separation: Microsoft 365 (OAuth-only mandatory, no separation possible once app passwords fully deprecated)
Anti-Spam & Anti-Virus
| Tool | Anti-Spam | Anti-Virus | DKIM | SPF | DMARC | ARC |
|---|---|---|---|---|---|---|
| Mailcow | Rspamd | ClamAV | Yes | Yes | Yes | Yes |
| Mailu | Rspamd | ClamAV | Yes | Yes | Yes | Yes |
| docker-mailserver | Rspamd/SA | ClamAV | Yes | Yes | Yes | Yes |
| iRedMail | Amavis+SA | ClamAV | Yes | Yes | Yes | No |
| Modoboa | Amavis+SA | ClamAV | Yes | Yes | Yes | No |
| Stalwart | Built-in | Milter | Yes | Yes | Yes | Yes |
| Maddy | DNSBL | External | Yes | Yes | Yes | No |
| Mail-in-a-Box | SA+Postgrey | Manual | Yes | Yes | Yes | No |
| Zimbra | Amavis+SA | ClamAV | Yes | Yes | Yes | No |
| Carbonio | Amavis+SA | ClamAV | Yes | Yes | Yes | No |
| Kerio Connect | Built-in | Add-on | Yes | Yes | Yes | No |
| Axigen | Built-in | Add-on | Yes | Yes | Yes | Yes |
| Google Workspace | Built-in | Built-in | Yes | Yes | Yes | Yes |
| Microsoft 365 | EOP | EOP | Yes | Yes | Yes | Yes |
| Proton Mail | Built-in | N/A* | Yes | Yes | Yes | No |
| Fastmail | Built-in | N/A | Yes | Yes | Yes | No |
| Zoho Mail | Built-in | N/A | Yes | Yes | Yes | No |
SA = SpamAssassin; EOP = Exchange Online Protection N/A* = encryption prevents server-side scanning Milter = external scanner via milter protocol
REST API Comparison
| Tool | API Type | Auth | Provisioning API |
|---|---|---|---|
| Mailcow | REST | API key | Full CRUD |
| Mailu | REST | API token | Full CRUD |
| docker-mailserver | None | N/A | CLI only |
| iRedMail | REST* | HTTP Basic | Full CRUD* |
| Modoboa | REST | Token | Full CRUD |
| Stalwart | REST | Bearer/key | Full CRUD |
| Maddy | None | N/A | CLI only |
| Mail-in-a-Box | REST | Basic/key | Full CRUD |
| Zimbra | SOAP | Token | Full CRUD |
| Carbonio | SOAP+REST | Token | Full CRUD |
| Kerio Connect | JSON-RPC | Session | Full CRUD |
| Axigen | REST+CLI | OAuth2 | Full CRUD |
| Google Workspace | REST | OAuth2 | Full CRUD |
| Microsoft 365 | REST | OAuth2 | Full CRUD |
| Proton Mail | None | N/A | Manual only |
| Fastmail | JMAP | Bearer | No admin API |
| Zoho Mail | REST | OAuth2 | Full CRUD |
* = iRedAdmin-Pro (paid) required for REST API
Best API: Google Workspace (Admin SDK), Microsoft 365 (Graph API), Mailcow (OpenAPI/Swagger), Stalwart (comprehensive REST), Mailu (OpenAPI)
No API: docker-mailserver, Maddy (CLI only), Proton Mail (no public admin API)
Monitoring Integration
| Tool | Prometheus | SNMP | Health EP | Logs |
|---|---|---|---|---|
| Mailcow | Exporter | No | Watchdog | Redis |
| Mailu | No | No | Docker HC | Stdout |
| docker-mailserver | No | No | Docker HC | Stdout |
| iRedMail | No | No | No | Files |
| Modoboa | No | No | No | RRD |
| Stalwart | Native | No | Yes | Stdout |
| Maddy | No | No | No | Stdout |
| Mail-in-a-Box | No | No | Status | Munin |
| Zimbra | No | No | No | Files |
| Carbonio | No | No | Consul | Files |
| Kerio Connect | No | No | No | MyKerio |
| Axigen | Native | Yes | Yes | Files |
| Google Workspace | No | No | Dashboard | API |
| Microsoft 365 | No | No | Dashboard | API |
| Proton Mail | No | No | No | No |
| Fastmail | No | No | No | No |
| Zoho Mail | No | No | No | API |
HC = Docker healthcheck
Best monitoring integration: Stalwart (native Prometheus + OpenTelemetry), Axigen (native Prometheus + SNMP), Mailcow (official Prometheus exporter + Watchdog)
Deployment and Licensing
| Tool | License | Docker | ARM64 | K8s | Min RAM |
|---|---|---|---|---|---|
| Mailcow | GPL-3.0 | Yes | No | No | 4 GB |
| Mailu | MIT | Yes | Yes | Yes | 1 GB |
| docker-mailserver | MIT | Yes | Yes | Helm | 512 MB |
| iRedMail | GPLv2 | Beta | Yes | No | 2 GB |
| Modoboa | ISC | Dev | No | No | 2 GB |
| Stalwart | AGPL-3.0 | Yes | Yes | Yes | 512 MB |
| Maddy | GPL-3.0 | Yes | Yes | No | 256 MB |
| Mail-in-a-Box | CC0 | No | No | No | 1 GB |
| Zimbra | CPAL/Prop | No | No | No | 16 GB |
| Carbonio | AGPL/Prop | Limited | No | No | 16 GB |
| Kerio Connect | Proprietary | No | No | No | 2 GB |
| Axigen | Proprietary | Yes | No | Yes | 1 GB |
| Google Workspace | Proprietary | N/A | N/A | N/A | N/A |
| Microsoft 365 | Proprietary | N/A | N/A | N/A | N/A |
| Proton Mail | Proprietary | N/A | N/A | N/A | N/A |
| Fastmail | Proprietary | N/A | N/A | N/A | N/A |
| Zoho Mail | Proprietary | N/A | N/A | N/A | N/A |
SaaS Pricing
| Tool | Entry Tier | Mid Tier | Storage |
|---|---|---|---|
| Google Workspace | $7/user/mo | $14/user/mo | 30 GB–5 TB |
| Microsoft 365 | $6/user/mo | $12/user/mo | 50–100 GB |
| Proton Mail | $6.99/user/mo | $9.99/user/mo | 15–50 GB |
| Fastmail | $6/user/mo | $10/user/mo | 60–100 GB |
| Zoho Mail | $1/user/mo | $4/user/mo | 5–50 GB |
Best value: Zoho Mail ($1/user/month entry) Best privacy: Proton Mail (E2E encryption, Swiss jurisdiction)
Tools
17 tools.
Axigen
Axigen is a commercial email, calendar, and collaboration server developed by Gecad Technologies (Romania), a company with roots in security software (the original developers of BitDefender).
License: Proprietary (proprietary) · Kind: web · Deploy: native · SSO: none
Carbonio
Carbonio is an email and collaboration platform developed by Zextras, an Italian company that was previously the primary third-party extension provider for Zimbra (Zextras Suite).
License: AGPL-3.0-only (OSS) · Kind: web · Deploy: native · SSO: none
docker-mailserver
docker-mailserver (DMS) is the most popular open-source containerized mail server, with over 17,000 GitHub stars.
License: MIT (OSS) · Kind: web · Deploy: native, docker · SSO: none
Fastmail
Fastmail is an independent, privacy-focused email provider headquartered in Melbourne, Australia. It has been operating since 1999, making it one of the longest-running independent email services.
License: Proprietary (proprietary) · Kind: web · Deploy: saas · SSO: OIDC, SAML
Google Workspace (Gmail)
Google Workspace is the dominant SaaS email and productivity platform, combining Gmail, Google Calendar, Google Drive, Docs, Sheets, Slides, and Meet into a single cloud suite.
License: Proprietary (proprietary) · Kind: web · Deploy: saas · SSO: OIDC, SAML
iRedMail
iRedMail is a long-established open-source mail server installer, in active development since 2007, with approximately 1,800 GitHub stars.
License: GPL-2.0-only (OSS) · Kind: web · Deploy: native · SSO: none
Kerio Connect
Kerio Connect (formerly Kerio MailServer) is a commercial email and collaboration server developed by Kerio Technologies, now a subsidiary of GFI Software.
License: Proprietary (proprietary) · Kind: web · Deploy: native · SSO: none
Maddy Mail Server
Maddy is a composable all-in-one mail server written entirely in Go that replaces the traditional stack of Postfix, Dovecot, OpenDKIM, OpenSPF, and OpenDMARC with a single daemon.
License: GPL-3.0-only (OSS) · Kind: web · Deploy: native, docker · SSO: none
Mail-in-a-Box
Mail-in-a-Box (MiaB) is a one-click, opinionated mail server deployment that automates the setup of a complete email infrastructure on a fresh Ubuntu 22.04 server.
License: CC0-1.0 (source-available) · Kind: web · Deploy: native · SSO: none
Mailcow
Mailcow (stylized “mailcow: dockerized”) is one of the most popular open-source, self-hosted email server platforms, with over 12,000 GitHub stars.
License: GPL-3.0-only (OSS) · Kind: web · Deploy: native, docker · SSO: none
Mailu
Mailu is a full-featured mail server distributed as a set of Docker images, with over 7,100 GitHub stars.
License: MIT (OSS) · Kind: web · Deploy: native, docker · SSO: none
Microsoft 365 (Exchange Online)
Microsoft 365 with Exchange Online is the dominant enterprise email platform, deeply integrated with the Microsoft ecosystem (Outlook, Teams, SharePoint, OneDrive, Entra ID).
License: Proprietary (proprietary) · Kind: web · Deploy: saas · SSO: OIDC, SAML
Modoboa
Modoboa is a mail hosting and management platform that provides a modern web UI on top of the traditional Postfix + Dovecot stack.
License: ISC (OSS) · Kind: web · Deploy: native · SSO: none
Proton Mail Business
Proton Mail is a privacy-focused, end-to-end encrypted email platform headquartered in Switzerland and operated by Proton AG.
License: Proprietary (proprietary) · Kind: web · Deploy: saas · SSO: OIDC, SAML
Stalwart Mail Server
Stalwart Mail Server is a modern, all-in-one mail and collaboration server written entirely in Rust.
License: AGPL-3.0-only (OSS) · Kind: web · Deploy: native, docker · SSO: none
Zimbra
Zimbra Collaboration is an enterprise email, calendar, and collaboration platform originally developed by Zimbra, Inc. (formerly LiquidSys) and first released in 2005.
License: Proprietary (proprietary) · Kind: web · Deploy: native · SSO: none
Zoho Mail
Zoho Mail is a business email platform that is part of the broader Zoho ecosystem – a suite of 40+ integrated SaaS applications including Zoho CRM, Zoho Desk, Zoho Projects, and Zoho One.
License: Proprietary (proprietary) · Kind: web · Deploy: saas · SSO: OIDC, SAML
