Comparison
PGP vs. S/MIME for Enterprise Email
PGP and S/MIME both use public-key cryptography to protect email, but they differ in key or certificate management, trust models and ecosystem expectations. Understanding these differences matters when an organization must exchange encrypted email with established partners.
Comparison at a glance
| Consideration | PGP | S/MIME |
|---|---|---|
| Trust and identity | Public-key distribution and verification model | X.509 certificates and CA-based trust model |
| Key discovery | Key exchange, directories and other configured methods | Certificate exchange, directory and CA-associated infrastructure |
| Encryption | Encrypt to the recipient’s public key | Encrypt using the recipient’s certificate and public key |
| Signing | Sender signing key | Sender signing key and certificate |
| Administrative needs | Key generation, exchange, imports, revocation and policy | Certificate issuance, discovery, expiration, renewal and policy |
| Compatibility | Requires a compatible PGP ecosystem | Requires a compatible S/MIME ecosystem |
Scroll sideways to see the whole table.
Both are open IETF standards. OpenPGP is specified in RFC 9580 (external link), and S/MIME version 4.0 in RFC 8551 (external link).
The right method depends on your recipients
Many organizations must continue using the protocol supported by their external partners or required by internal standards. A cloud platform supporting both can help centralize policy and operational workflows, but it does not erase protocol compatibility differences: a PGP message still needs a recipient with a PGP key, and an S/MIME message still needs a recipient certificate.
See Cloud PGP and Cloud S/MIME for how each standard is handled in the hosted model.
Transport encryption is not the same as message encryption
TLS protects the connection between two communicating systems, such as mail servers. Once the message arrives, TLS no longer protects it, and each server along the path can read it.
PGP and S/MIME encrypt the message content itself for the intended key holders. The content stays encrypted in mailboxes and backups until a holder of the right private key decrypts it.
Secure web portals and encrypted documents are different mechanisms again. A portal controls access to a message stored for retrieval, and an encrypted document protects an attachment with a password or code. The delivery methods table compares what each one protects.
Frequently asked questions
Can PGP and S/MIME coexist?
Yes. An organization can use PGP with some partners and S/MIME with others. A platform that supports both can apply the appropriate method per recipient or policy, but each exchange still requires that both sides support the same standard.
Is a digital signature the same as encryption?
No. A signature lets the recipient check that a message came from the holder of the signing key and was not changed after signing. It does not hide the content. Encryption protects confidentiality. A message can be signed, encrypted, or both, in PGP and in S/MIME.
What happens when a partner has no key?
If no PGP public key or S/MIME certificate can be found for a recipient, the message cannot be encrypted to them with that standard. Depending on policy, the platform can use a supported alternative such as validated TLS delivery, a secure web portal or an encrypted document, or handle the message according to configured rules. These alternatives offer different protection from PGP or S/MIME. See How It Works.
What is the role of a certificate authority?
In S/MIME, a certificate authority (CA) issues X.509 certificates that bind a public key to an identity such as an email address. The recipient’s software checks the certificate chain up to a root CA it trusts. Certificates from widely recognized public CAs are usually trusted by default; certificates from a private CA are trusted only where its root has been installed. PGP does not rely on certificate authorities in the same way. See Cloud S/MIME.
Not sure which standard your partners need?
Contact us to discuss PGP, S/MIME and mixed environments.