SquirrelMail

What SquirrelMail does

SquirrelMail is an open-source, PHP-based webmail client founded in 1999 that provides browser-based email access by connecting to IMAP and SMTP servers. The product is distributed free of charge under the GNU General Public License version 2 and is maintained by The SquirrelMail Project Team, a volunteer community that releases the software via SourceForge.net. SquirrelMail supports a broad range of IMAP backends including Cyrus, UW IMAP, Courier, Dovecot, Binc IMAP, DBMail, Exchange, hMailServer, and Mercury32, with optional MySQL or PostgreSQL backends for user preferences and LDAP integration for address books. The codebase is extensible through a documented plugin architecture that has accumulated dozens of community-contributed extensions covering security (Password Forget, S/MIME Verification, Virtual Keyboard, Yubikey authentication), usability (Autocomplete, Compose Extras), and account administration (VPOPMail Account Administration). Internationalization covers 20+ languages and over 50 character encodings including UTF-8, ISO-8859 variants, Windows-125x, KOI8, and CJK sets.

The project operates without commercial monetization: there are no paid tiers, subscriptions, enterprise editions, or institutional investors. The go-to-market is purely community-led, relying on SourceForge distribution, mailing lists, IRC, and documentation portals to drive voluntary adoption by system administrators and self-hosting organizations. Paul Lesniewski has served as the primary public-facing maintainer, with Jonathan Angliss sponsoring the domain and security certificates. Strategic activity has slowed materially — the last substantive release was PHP 8 compatibility in October 2021, the site copyright extends only to 2016, and the project is best characterized as in maintenance mode rather than active development. There are no disclosed funding rounds, no headquarters beyond a mailing address in New York, and the 1-10 "employees" listed are volunteer contributors rather than paid staff.

Name

SquirrelMail

Legal name

The SquirrelMail Project Team

Website

https://squirrelmail.org

Company type

Private

Founded year

1999

Operating status

Operating

Headcount range

1–10 employees

Short description

SquirrelMail is a free, open-source PHP-based webmail client founded in 1999 that provides browser-based email access by connecting to external IMAP servers, serving system administrators and self-hosting organizations worldwide. It is maintained by a volunteer community under GPL v2.

Ownership category

akta.pro rank

Headquarters

HQ city

New York

HQ country

United States

HQ region

North America

Markets served

GTM type

B2B

Offering type

Software

Cost components

Personnel, Infrastructure, Technology or R&D, Operations

Revenue model

1. Open Source Distribution: SquirrelMail is distributed free of charge under GNU General Public License v2. No commercial revenue is generated. The project operates as a volunteer community effort with no direct monetization.

Pricing tiers

Go-to-market motion1 record

Distribution channels1 record

Marketing channels5 records

Core offering

SquirrelMail is a standards-based, PHP-written webmail package that provides a browser-based interface for accessing and managing email stored on IMAP servers. It supports email reading, composing, sending, folder management, address books, message filtering, and server-side sorting/threading. The product is distributed as free open-source software under GNU GPL v2 and is extensible through a modular plugin architecture.

Product overview

SquirrelMail is a single, unified PHP-based webmail application that provides browser-based email access by connecting to external IMAP servers. The core product is a standalone webmail interface (versions 1.4.x stable) that offers email reading, composing, folder management, address books, and preferences. The product is extensible through a plugin architecture, with the Compatibility Plugin being a foundational add-on that enables other plugins to function across versions. Official plugins include the Password Forget Plugin (security), S/MIME Verification Plugin (security), Autocomplete Plugin (usability), Compose Extras Plugin (usability), Custom From Plugin (identity), Virtual Keyboard Plugin (security), Windows Plugin (UI), VPOPMail Account Administration Plugin (account management), and User Information Plugin (utility). Documentation suite includes the Administrator's Manual, Developer's Manual, User's Manual, and Translator's Manual. Licensed under GNU GPL v2.

Differentiator

Problem solved

Functional benefit

Products and services

• SquirrelMail Webmail Interface A PHP-based webmail client that provides a web interface for accessing and managing email via IMAP servers. Supports reading, composing, sending emails, folder management, address books, and message filtering. Targeted at system administrators and IT organizations that want self-hosted, customizable webmail with broad IMAP server compatibility.

Quantifiable outcome

• Supports over 50 character encodings including UTF-8, all ISO-8859 variants, Windows-125x, KOI8, and CJK character sets

Segments2 records

Ideal customer profiles1 record

Technology focussed Yes

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Integration9 records

Feature6 records

Partnerships

Two partnerships are on record, tiered core and minor.

• SourceForge.netcoreGTM or Marketing PartnerSourceForge.net provides the SquirrelMail project with repository hosting, bug trackers, mailing lists, release distributions, and other development services. It is the world's largest open source software development website, hosting over 100,000 projects with over 1,000,000 registered users.
• Jonathan AnglissminorGTM or Marketing PartnerSquirrelMail Project Team member who sponsors the project by providing the domain name and security certificates. Also contributes coding and development work.

Scale indicators3 records

Recent moves5 records

Expansion highlights3 records

Broad incumbents

• iRedMail: Open-source mail server bundle (Postfix/Dovecot, etc.) often paired with Roundcube or SOGo as the webmail front-end; competes for the same self-hosted mail deployment budget as SquirrelMail at a fuller-stack level.
• Citadel Groupware: Open-source groupware suite that includes a webmail interface and supports IMAP/SMTP; serves similar self-hosted institutional and community-organization deployments as SquirrelMail with broader messaging features.
• Zimbra Collaboration (Synacor): Open-source-derived email and collaboration platform with a webmail front-end; broader in scope than SquirrelMail (mail, calendar, contacts, admin console) but serves the same self-hosted institutional customer base.

Direct peers

• SOGo: Open-source groupware and webmail front-end that connects to IMAP/SMTP servers such as Dovecot and Cyrus; comparable to SquirrelMail in self-hosted webmail deployment but extends into calendar and address book sync, making it a fuller alternative for institutions.
• AfterLogic WebMail Lite: Open-source PHP webmail client with a self-hosted edition that targets the same sysadmin persona as SquirrelMail; supports IMAP backends and offers a more modern UI while remaining lightweight to deploy.
• Horde Webmail: Long-running open-source webmail and groupware suite (IMP webmail component) written in PHP; predates many modern webmail clients and serves the same institutional, self-hosted IMAP-based deployments as SquirrelMail.
• RainLoop Webmail: Lightweight open-source PHP webmail client that supports IMAP/SMTP backends with a modern AJAX interface; competes for the same self-hosted webmail deployments as SquirrelMail, particularly among small organizations seeking simpler installation.
• SnappyMail: Open-source lightweight webmail client (community fork that succeeded RainLoop Lite); offers a modernized alternative targeting the same self-hosted webmail niche as SquirrelMail with active maintenance.
• Roundcube Webmail: Open-source PHP-based webmail client that connects to IMAP servers; the closest modern functional and architectural analog to SquirrelMail, sharing the same target customer (system administrators self-hosting email) and the same PHP/MYSQL/PostgreSQL deployment model.

Emerging players

• Mailpile: Open-source privacy-focused webmail client aimed at encrypted, self-hosted email; overlaps with SquirrelMail in the self-hosted segment but differentiates on modern cryptography and a contemporary UI, appealing to privacy-first users.

Market position

Strengths4 records

Weaknesses4 records

Competitive moat4 records

Key risks6 records

Key highlights6 records

Customer concentration

Revenue estimate

Valuation estimate

Number of profiles

Profiles1 record

Funding overview

Funding rounds

Investors

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about SquirrelMail