gpg4o

gpg4o is an Outlook add-in for people who need OpenPGP encryption and signing in a Windows email workflow. Its strongest case is combining message protection with key and enterprise administration options; its Outlook focus and exposed email metadata make it a poor fit for users who need broader platform coverage or concealed headers.

Overview

Using asymmetric public and private keys, gpg4o encrypts and decrypts email and attachments, and lets users sign and check messages. It supports encrypted HTML email, PGP/MIME and PGP/Inline, giving teams several OpenPGP mail formats to work with. Encryption protects message text and attachments, but not the subject line or recipient list, so sensitive context should not go in those fields.

Compatibility with Symantec Encryption, Enigmail, KMail, Apple Mail, K9-Mail and iPGMail may help when exchanging protected messages across different mail clients. BAYOOSOFT is based in Darmstadt, Germany, was founded in 2001, and cites Security Made in Germany by Teletrust, ISO 9001 quality management and a TISAX assessment.

Key features

• OpenPGP encryption and signatures: Encrypt, decrypt, sign and check messages and attachments from Outlook. This suits correspondents already working with public-key encryption, but it does not conceal subject lines or recipient lists.
• Key Server Management: Automatic synchronization, local and public key servers, and Web of Trust checking can support ongoing key handling. Central management requires Enterprise KeyServer, an additional requirement for organizations that need a centrally administered setup.
• Enterprise controls: Support for terminal servers, Microsoft Policy Manager, automatic key generation and working groups makes gpg4o more relevant to managed environments than a basic personal encryption add-in.
• License and maintenance: A license can be used on several computers and profiles if the licensed email address is configured in Outlook on each one. Once maintenance expires, encrypted and signed email remains usable, but updates stop.
• Support: Users can contact support or open the gpg4o Help menu in Outlook, which sends a log file automatically. BAYOOSOFT says these logs contain no personal information, passwords or email contents.

Pricing

The pricing model includes a free version and paid plans. The free plan costs nothing, has no time limit and offers limited functionality. It is a way to start without a subscription, but users who need all OpenPGP encryption functions must move to the paid gpg4o plan.

The gpg4o plan is €99.95 a month and includes all functions of the OpenPGP encryption system. Its stated compatibility covers Microsoft Outlook 2016, 2019, 2021 and 365 Classic. The feature page's current supported desktop requirements are narrower: Outlook 2024 or 365 Classic on Windows 11, with Mac OS unsupported. Buyers should check that their Outlook and Windows combination matches the current requirements before committing.

Two maintenance extensions are available: gpg4o – Extension product maintenance 1 year costs €5,195 a year, billed one year, while gpg4o – Extension product maintenance 3 years costs €13,995 a year, billed three years. Both provide updates and support for gpg4o. A 180-day trial is also offered. The extension prices are substantial relative to the monthly plan, so they warrant careful review by organizations planning continued maintenance.

Platforms

gpg4o is for Windows and works as a Microsoft Outlook add-in. The current feature page supports Outlook 2024 or 365 Classic on Windows 11 and marks Mac OS unsupported. There is no Gmail integration, making it unsuitable for a Gmail-centered workflow or users seeking a cross-platform email tool.

Who it's for

gpg4o is best suited to professionals and private users who exchange confidential information through compatible Outlook installations and want OpenPGP encryption, signatures and key-management capabilities. Its terminal-server, policy-management and working-group features strengthen its case for organizations. It is not the right choice for anyone who needs to hide recipients or subject lines, or needs native support beyond Windows Outlook.

Pros and cons

Pros

• Multiple OpenPGP mail formats: HTML email, PGP/MIME and PGP/Inline support gives users flexibility when handling protected messages.
• Substantial key and administration options: Key servers, Web of Trust checking, automatic key generation and Microsoft Policy Manager support address needs beyond basic encryption.
• Continued use after maintenance expires: Users can still send and read encrypted or signed email, even though updates cease.

Cons

• Metadata stays exposed: Subject lines and recipient lists remain unencrypted, limiting protection for sensitive routing and context.
• Narrow platform fit: Current support is Windows 11 with Outlook 2024 or 365 Classic, and Mac OS is unsupported.
• Central management has an extra requirement: Enterprise KeyServer is needed for centralized key management.
• Maintenance extensions carry high stated prices: The one- and three-year options cost €5,195 a year and €13,995 a year respectively.

Alternatives

For a broader shortlist, browse Email Encryption Software or File encryption tools.

• Lockbin is worth considering if Linux, macOS or web access matters; its free plan covers one user, 25 MB attachments and six months of inbox storage.
• FlowCrypt may suit an extension-based workflow, with a free plan for fewer than 100 users and a 5 MB attachment threshold; its Enterprise plan supports attachments up to 25 MB and more than 100 users.
• SecureMyEmail fits users seeking coverage across Windows, macOS, iOS and Android; its free plan covers one email address.
• c.Email is an alternative for users who want a free extension with unlimited email addresses and support for existing email addresses.
• Proofpoint Email DLP and Encryption is a paid option with Android, iOS, web and Windows platforms.
• DataMotion Secure Email Exchange is an enterprise offering with custom pricing and Android, API, iOS and web platforms.
• Virtru Email Encryption may suit users who need web, Windows, macOS, iOS or Android coverage; its Starter and Business plans each cover five users and are billed annually.
• RMail is another paid option, with personal, standard and business plans measured in monthly units.

Verdict

Choose gpg4o if your confidential email work belongs in a supported Windows Outlook setup and you want OpenPGP encryption alongside key and enterprise administration features. Its Outlook integration and breadth of key controls are the main reasons to choose it; the exposed subject and recipient metadata, Windows-only support and separate central-management requirement are good reasons to look elsewhere.