Sample code for 30+ languages & platforms
Swift

Load .eml and Decrypt (smime.p7m)

Loads an encrypted email from a .eml file and decrypts using certificate w/ private key found in a .p12 (or .pfx) file.

The Content-Type and Content-Disposition email headers of the email to be decrypted look similar to this:

Content-Type: application/x-pkcs7-mime; smime-type=enveloped-data;
	name="smime.p7m"
Content-Disposition: attachment; filename="smime.p7m"

Chilkat Swift Downloads

Swift

func chilkatTest() {
    var success: Bool = false

    let email = CkoEmail()!

    // Add a PFX (or .p12) to be used for decryption
    success = email.addPfxSourceFile(pfxFilePath: "myCert.p12", password: "passwordForP12")
    if success != true {
        print("\(email.lastErrorText!)")
        return
    }

    // Loading the .eml automatically decrypts.
    success = email.loadEml(mimePath: "encrypted.eml")
    if success != true {
        print("\(email.lastErrorText!)")
        return
    }

    // The email now exists as it was prior to encryption.
    // Your app may access the email's subject, body, attachments,
    // etc. using the Chilkat Email API...

    // Save the decrypted email:
    success = email.saveEml(path: "decrypted.eml")
    if success != true {
        print("\(email.lastErrorText!)")
        return
    }

    print("Success.")

}