Horde IMP
What Horde IMP is
Horde IMP is a free, open-source PHP webmail client that provides browser access to IMAP and POP3 accounts. It offers dynamic, mobile, basic, and minimal text-only interfaces for different browsers and devices. Message composition supports HTML through a cross-browser WYSIWYG editor, HTML signatures, and drag-and-drop attachments. Mail features include search, address autocompletion, spell checking, threaded conversations, mailbox previews, and forwarding multiple messages at once. Users can manage IMAP folders, shared-folder access controls, subscriptions, multiple identities, and mailbox quotas. IMP integrates with Horde’s Ingo filtering, Turba address book, and Kronolith calendar applications, and calendar tools are included. S/MIME and PGP encryption and signatures are supported, with OpenSSL required for those connections. Installation requires a working Horde setup, PHP file-upload support, an IMAP or POP3 server, and Sendmail or SMTP. With POP3, on-demand filtering, searching, and sorting are disabled, and the server must support UIDL. The project recommends PEAR installation and documents Git installation for development code or unreleased fixes.
Who it suits
IMP suits users or administrators who need self-hosted webmail for IMAP or POP3 accounts and can provide the required Horde and mail-server infrastructure. It also fits deployments needing multiple browser interfaces and encryption options.
What it does well
- Supports IMAP and POP3 browser access
- Includes HTML composition and drag-and-drop attachments
- Offers S/MIME and PGP encryption and signatures
- Integrates with Horde filtering, contacts, and calendar apps
- Provides mobile and text-only browser interfaces
What to know first
- Requires a working Horde installation
- Needs an IMAP or POP3 server and mail transport
- POP3 disables on-demand filtering, searching, and sorting
- OpenSSL is required for specified secure connections
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| IMP | Open source webmail application; requires a Horde installation and an IMAP or POP3 server | Free |
As horde.org lists them, read 12 Oct 2026. The maker's own page has the final word.
Verdict
Horde IMP provides a broad, self-hosted webmail feature set with multiple interfaces and Horde integrations. Its infrastructure prerequisites and POP3 limitations should be checked before deployment.
Facts from Horde IMP's own pages
- App coverage
- web · horde.org, 23 Sept 2026
- Browser views
- It provides dynamic, mobile, basic, and minimal text-only interfaces for different browsers and devices. · horde.org, 12 Oct 2026
- Calendar tools
- Yes · horde.org, 23 Sept 2026
- Composition
- Features include HTML composition with a cross-browser WYSIWYG editor, HTML signatures, and drag-and-drop attachment support. · horde.org, 12 Oct 2026
- Encryption
- IMP supports S/MIME and PGP-based encryption and signatures; OpenSSL is required for S/MIME and for TLS or SSL connections to mail servers. · horde.org, 12 Oct 2026
- Free plan
- Yes · horde.org, 23 Sept 2026
- Installation
- The guide recommends installation through PEAR and also documents installation from Git for development code or unreleased fixes. · horde.org, 12 Oct 2026
- Integrations
- The feature list names integration with Horde's Ingo email filtering, Turba address book, and Kronolith calendar applications. · horde.org, 12 Oct 2026
- Mailbox management
- It supports IMAP folders, shared-folder ACL management, folder subscriptions, multiple identities, and mailbox quotas. · horde.org, 12 Oct 2026
- Mail tools
- Features include flexible message search, address autocompletion, spell checking, thread view, mailbox previews, and forwarding multiple messages at once. · horde.org, 12 Oct 2026
- Open source
- The project describes IMP as OSI Certified Open Source Software. · horde.org, 12 Oct 2026
- POP3 limit
- With POP3, on-demand filtering, searching, and sorting are disabled, and the POP server must support UIDL. · horde.org, 12 Oct 2026
- Prerequisites
- IMP requires a working Horde installation, PHP file-upload support, at least one IMAP or POP3 server, and Sendmail or an SMTP server. · horde.org, 12 Oct 2026
- Purpose
- IMP is a PHP webmail client that provides browser access to IMAP and POP3 accounts. · horde.org, 12 Oct 2026
- Security configuration
- The installation guide recommends SSL for browser-to-web-server traffic and TLS or a private network for web-server-to-mail-server traffic; TLS is the default mail-server connection configuration described there. · horde.org, 12 Oct 2026
- Support
- The project points users to its FAQ, application mailing lists, and occasional IRC support from Horde developers, contributors, and users. · horde.org, 12 Oct 2026
Where Horde IMP stands on Freedom251
- Email clients#39 of 142