Why Can't I Encrypt Email in Apple Mail?

If Apple Mail lets you sign messages but not encrypt them, the most likely explanation is not that Apple Mail forgot how S/MIME works. The more likely explanation is that one of encryption’s extra prerequisites is missing.

The first question to ask

Do you have the recipient’s public certificate?

That question solves more Apple Mail encryption mysteries than almost any other.

Why your own certificate is not enough

Your own S/MIME certificate helps with:

• signing your outbound mail
• identifying yourself in certificate-backed workflows

It does not automatically give you what you need to encrypt mail to someone else. Encryption requires the recipient’s public certificate so the message can be encrypted for that recipient.

Other reasons encryption may be unavailable

• the issuing chain is not trusted
• the certificate identity does not match the active account
• the imported identity is incomplete
• Apple Mail does not see a usable recipient certificate

What to do next

1. confirm your own identity is usable for signing
2. confirm recipient certificate availability
3. confirm trust-chain status if private CA material is involved
4. verify account identity alignment

Practical takeaway

If encryption is unavailable while signing works, focus on the recipient side of the trust model first. That is where the missing condition usually lives.