gpg4o vs Secure Message

gpg4o is a Microsoft Outlook add-in for encrypting, decrypting, signing, and checking messages and attachments. It uses public and private keys under the OpenPGP standard, and supports encrypted HTML email, PGP/MIME, and PGP/Inline. Its key management can synchronize keys, use local or public key servers, and check the Web of Trust; central management requires Enterprise KeyServer. The product also supports terminal servers, Microsoft Policy Manager, automatic key generation, and working groups. When encryption is enabled, it protects message text and attachments, but not the subject line or recipient list. The current feature page lists Outlook 2024 or 365 Classic on Windows 11 and marks Mac OS unsupported. A limited free version is available without a time limit, and a 180-day trial is noted. The listed gpg4o plan costs €99.95 a month. After maintenance expires, users can still send and read encrypted or signed email, but they do not receive further updates.

Secure Message is a self-hosted inbound email gateway that filters mail before it reaches an existing mail server. Its Community features include Postfix content filtering, spam scoring, DNSBL, SPF, DKIM and DMARC checks, quarantine, mail logs and administrator MFA. Professional adds a recipient web portal: recipients open protected messages with a one-time code, without an account or app. Its rules can encrypt, redirect or block sensitive outbound messages, and recipient checks can use SMTP callout, LDAP or directory lookups. Stored messages, attachments and quarantine use Fernet encryption with AES-128-CBC and HMAC-SHA256; the key remains on the customer host. Access controls include TOTP administrator MFA, role-based access and audit logging, with logs exportable to CSV. Enterprise adds AI Autopilot tuning, eDiscovery and archive search, DLP and disclaimers; Autopilot and the classifier are off by default. The gateway can sit in front of Microsoft 365 or an existing mail server without mailbox migration. The single-node appliance runs on Debian 13, with 2 vCPU and 4 GB RAM recommended as a starting point.