SquirrelMail Technology Intelligence

What is SquirrelMail?

SquirrelMail is an open-source webmail application written in PHP that provides access to email via any web browser. Created in 1999, it became one of the most widely deployed webmail solutions due to its simplicity, stability, and minimal server requirements.

Unlike JavaScript-heavy webmail clients, SquirrelMail uses a lightweight, standards-based approach that works in virtually any browser, including text-based browsers and older systems. Each action results in a full page load, making it highly compatible but less dynamic than modern alternatives.

SquirrelMail connects to IMAP servers and supports SMTP for sending. Its plugin architecture allows customization, and it includes address book functionality, folder management, and attachment handling. While considered dated by modern standards, it remains in use where simplicity and compatibility are priorities.

SquirrelMail Features

IMAP Support: Full IMAP protocol. Folder subscriptions. Server-side storage. Multiple folder views. Quota display.

Compose: HTML and plain text. Multiple attachments. Address book integration. Draft saving. CC and BCC.

Address Book: Personal contacts. LDAP integration. vCard support. Search functionality. Import/export.

Folders: Folder management. Create, rename, delete. Subscription control. Nested folders. Special folder assignment.

Plugins: Plugin architecture. Calendar plugins. Spell check. Quota plugins. Theme plugins. Filters.

Languages: 50+ language translations. RTL support. Character set handling. Locale settings.

SquirrelMail Use Cases

Low-Resource Servers: Minimal hosting requirements. Shared hosting. Low-bandwidth environments. Basic VPS setups.

Legacy Systems: Older browser support. Text-based access. Accessibility focus. Compatibility requirements.

Educational: Student email systems. University webmail. Learning email protocols. Teaching environments.

Small Organizations: Small business email. Non-profit webmail. Community organizations. Local ISPs.

Backup Webmail: Secondary access method. Fallback system. Alternative to primary client. Emergency access.

Privacy-Focused: Self-hosted email. No JavaScript dependency. Minimal tracking. Simple audit.

SquirrelMail Code Examples

Configuration

// config/config.php
$domain = 'example.com';
$imapServerAddress = 'localhost';
$imapPort = 143;
$imap_server_type = 'dovecot';
$useSendmail = false;
$smtpServerAddress = 'localhost';
$smtpPort = 25;

// Authentication
$smtp_auth_mech = 'login';
$imap_auth_mech = 'login';

// Organization settings
$org_name = "My Organization";
$org_logo = SM_PATH . 'images/sm_logo.png';
$org_title = "SquirrelMail";

// Data directories
$data_dir = '/var/lib/squirrelmail/data/';
$attachment_dir = '/var/lib/squirrelmail/attach/';

Plugin Hook Example

// plugins/myplugin/setup.php
function squirrelmail_plugin_init_myplugin() {
    global $squirrelmail_plugin_hooks;

    $squirrelmail_plugin_hooks['compose_send']['myplugin'] = 'myplugin_compose_send';
    $squirrelmail_plugin_hooks['read_body_top']['myplugin'] = 'myplugin_read_body';
}

function myplugin_compose_send() {
    // Modify outgoing message
}

function myplugin_read_body() {
    // Add content when reading messages
}

SquirrelMail Benefits

Universal Compatibility: Works in any browser. No JavaScript required. Text browser support. Maximum accessibility.

Lightweight: Minimal server requirements. Low memory usage. Fast on basic hardware. Efficient performance.

Stable: Mature codebase. Well-tested. Production-proven. Predictable behavior.

Simple Setup: Easy installation. Configuration wizard. Clear documentation. Minimal dependencies.

Open Source: GPL licensed. Community maintained. Transparent code. No licensing costs.

Extensible: Plugin system. Custom themes. Hook architecture. Modular design.