gpg4o
gpg4o · Darmstadt, Germany · founded 2001
What it is
gpg4o is a Windows add-in for Microsoft Outlook that encrypts and decrypts messages and attachments, and can sign or check them. It uses public and private keys under the OpenPGP standard and supports encrypted HTML email, PGP/MIME, and PGP/Inline. Key Server Management can synchronize keys, use local and public key servers, and check Web of Trust relationships; central management requires Enterprise KeyServer. Additional capabilities include terminal server support, Microsoft Policy Manager, automatic key generation, and working groups. The maker lists compatibility with Symantec Encryption, Enigmail, KMail, Apple Mail, K9-Mail, and iPGMail. When encryption is enabled, message text and attachments are protected, but subject lines and recipient lists remain unencrypted. The current feature page lists Microsoft Outlook 2024 or 365 Classic on Windows 11 and marks Mac OS unsupported. A limited free version has no time limit, and a 180-day trial is noted. The listed gpg4o plan costs €99.95 a month. After maintenance expires, users can continue sending and reading protected email, but updates are no longer provided.
For and against
For
- Supports encrypted HTML, PGP/MIME, and PGP/Inline.
- Key management supports synchronization and Web of Trust checks.
- Supports signing and checking messages.
- A limited free version is available without a time limit.
Against
- Subject lines and recipient lists remain unencrypted.
- Mac OS is marked unsupported.
- Central key management requires Enterprise KeyServer.
- The listed paid plan is €99.95 a month.
The verdict
gpg4o offers Outlook-based OpenPGP tools with several email formats and key-management options. Users should account for the unencrypted subject and recipient fields and check compatibility with their Outlook and Windows versions.
Who it suits
It suits Outlook users on Windows who need OpenPGP encryption, signing, or message checking. It is positioned for professional confidential communication and private sharing of sensitive information.
Plans and prices
gpg4o Free
Free version without a time limit · Functionality is limited
Read 20 Sep 2026 · download.giepa.de
gpg4o – Extension product maintenance 1 year
Updates and support for gpg4o
Read 28 Sep 2026 · bayoosoft.com
gpg4o – Extension product maintenance 3 years
Updates and support for gpg4o
Read 28 Sep 2026 · bayoosoft.com
gpg4o
Microsoft Outlook 2016/2019/2021/365 Classic · OpenPGP functions
Read 28 Sep 2026 · bayoosoft.com
On the record
- Admin access controls
- Yesbayoosoft.com · read 20 Sep 2026
- Compatibility
- The maker lists compatibility with Symantec Encryption, Enigmail, KMail, Apple Mail, K9-Mail and iPGMail.bayoosoft.com · read 28 Sep 2026
- Encryption
- It uses asymmetric encryption with private and public keys and follows the OpenPGP standard.bayoosoft.com · read 28 Sep 2026
- Encryption boundary
- When encryption is enabled, the message text and attachments are protected but the subject line and recipient list remain unencrypted.bayoosoft.com · read 28 Sep 2026
- Enterprise features
- gpg4o supports terminal servers, Microsoft Policy Manager, automatic key generation and working groups.bayoosoft.com · read 28 Sep 2026
- Gmail integration
- Nobayoosoft.com · read 20 Sep 2026
- Key management
- Key Server Management supports automatic synchronization, local and public key servers, and Web of Trust checking; central management requires Enterprise KeyServer.bayoosoft.com · read 28 Sep 2026
- License use
- A license can be used on several computers and profiles when the licensed email address is configured in Outlook on each computer.bayoosoft.com · read 28 Sep 2026
- Log privacy
- The maker says gpg4o log files contain no personal information, passwords or email contents.bayoosoft.com · read 28 Sep 2026
- Mail formats
- It supports encrypted HTML email, PGP/MIME and PGP/Inline.bayoosoft.com · read 28 Sep 2026
- Maintenance expiry
- After maintenance expires, users can continue sending and reading encrypted or signed email but receive no further updates.bayoosoft.com · read 28 Sep 2026
- Message expiry
- Nobayoosoft.com · read 20 Sep 2026
- Outlook integration
- The add-in provides end-to-end encryption directly through the Outlook interface.bayoosoft.com · read 28 Sep 2026
- Product
- gpg4o is a Microsoft Outlook add-in for encrypting, decrypting, signing and checking messages and attachments.bayoosoft.com · read 28 Sep 2026
- Recipient verification
- identitybayoosoft.com · read 20 Sep 2026
- Secure delivery
- attachmentbayoosoft.com · read 20 Sep 2026
- Support
- Technical support is available through the contact process or the gpg4o Help menu in Outlook, with a log file sent automatically.bayoosoft.com · read 28 Sep 2026
- Supported desktop
- The current feature page lists Microsoft Outlook 2024 or 365 Classic on Windows 11 and marks Mac OS unsupported.bayoosoft.com · read 28 Sep 2026
