gpg4o

gpg4o is an OpenPGP add-in for Microsoft Outlook. It suits Windows users and organizations that need encrypted email, signatures and centralized key-management options. Its strengths are Outlook integration and enterprise controls; exposed email headers and the lack of Mac support are important limits.

Overview

gpg4o encrypts and decrypts messages and attachments, and lets Outlook users sign messages and check signatures using public and private keys. It supports encrypted HTML email, PGP/MIME and PGP/Inline, and the maker cites compatibility with Symantec Encryption, Enigmail, KMail, Apple Mail, K9-Mail and iPGMail. That range can help when correspondents use different OpenPGP-capable clients.

Encryption protects message text and attachments, not the subject line or recipient list. Keep sensitive details out of those fields. gpg4o is built around Outlook rather than general email coverage, and Gmail integration is not supported.

Key features

• Key Server Management: Automatic synchronization, local and public key servers, and Web of Trust checking help users manage keys. Central management requires Enterprise KeyServer, so organizations needing that capability should account for it separately.
• Enterprise administration: Terminal-server support, Microsoft Policy Manager, automatic key generation and working groups make gpg4o more suitable for managed deployments than a basic email-encryption add-in.
• Multi-computer licensing: A license can be used on several computers and profiles if the licensed email address is configured in Outlook on each one.
• Support and maintenance: Support is available through the contact process or Outlook's Help menu, which sends a log file automatically. The maker says logs contain no personal information, passwords or email contents. After maintenance expires, sending and reading encrypted or signed email continues, but updates stop.

Pricing

The pricing model is freemium, with a free version and a 180-day trial. The paid plan is labeled gpg4o and costs €99.95 a month. It includes all functions of the OpenPGP encryption system and supports Microsoft Outlook 2016, 2019, 2021 and 365 Classic. This is the full-featured choice for users who need the complete encryption system, though the monthly price is a substantial ongoing commitment.

gpg4o Free costs nothing, has no time limit and offers limited functionality. It may suit someone wanting a continuing free option, but the feature limits make it a weaker fit where full OpenPGP functionality is required.

Maintenance extensions cover updates and support: the one-year option costs €5,195 a year and the three-year option costs €13,995 a year, billed one year and three years respectively. Maintenance is relevant to buyers who want continued updates and support; core encrypted and signed mail use continues after it expires.

Platforms

The current supported desktop combination is Microsoft Outlook 2024 or 365 Classic on Windows 11. Mac OS is unsupported. The paid plan also names Outlook 2016, 2019 and 2021, so buyers should confirm that their specific Outlook and Windows setup matches the current compatibility requirements before committing. The product does not integrate with Gmail.

Who it's for

gpg4o is a sensible choice for Windows-based professionals and organizations that already use Outlook and need OpenPGP protection, signature checking, or key administration. Enterprise KeyServer and policy-related features matter most to administrators managing teams. It is a poor fit for Mac users, Gmail workflows, or anyone who needs recipient lists and subject lines encrypted.

Pros and cons

• Pro: Supports multiple OpenPGP mail formats and lists compatibility with several other mail clients, giving teams options when exchanging protected messages.
• Pro: Key-server, working-group and policy features support organizational administration beyond basic encryption.
• Pro: Licensed users can use the software on several computers and profiles when the licensed address is configured in Outlook on each.
• Con: Subject lines and recipient lists remain unencrypted, exposing message context even when the body and attachments are protected.
• Con: Mac OS and Gmail are unsupported, limiting it to a narrower set of email setups.
• Con: Central key management requires Enterprise KeyServer, and continued updates require active maintenance.

Alternatives

For a wider range of platforms, Lockbin supports Linux, macOS, web and Windows, with a free plan for one user, 25 MB attachments and six months of inbox storage. Send It Secure is another freemium option, with API, extension, iOS, web and Windows support; its Guest plan includes 30-day retention, 25 MB files and 10 lifetime message sends to non-paid users.

SecureMyEmail supports Android, iOS, macOS and Windows, and its free plan covers one email address. Secure Message offers Linux, self-hosted and web deployment, making it an option to consider for those environments. c.Email is a free extension with support for existing email addresses and unlimited addresses.

FlowCrypt is an extension option with a free plan for fewer than 100 users and a 5 MB attachment threshold; its enterprise plan raises the attachment limit to 25 MB and is aimed at larger deployments. Mimecast Secure Messaging offers web, mobile, desktop and Windows platforms. DataMotion Secure Email Exchange is an enterprise offering with Android, iOS, web and API support.

Browse more options in Email Encryption Software and File encryption tools.

Verdict

Choose gpg4o if your work is centered on supported Windows versions of Outlook and you need OpenPGP encryption, signatures and organizational key controls. Its Outlook integration and enterprise features are the main reasons to select it. Look elsewhere if you need Mac or Gmail support, or if your security requirements include hiding recipient lists and subject lines.