S/MIME带签名邮件未经加密就无法正常工作。

使用以下代码将S/MIME电子邮件加密和签名：

from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.application import MIMEApplication
import smtplib
from OpenSSL import crypto

def send_signed_email(sender_email, recipient_email, subject, body, attachments, signing_key_file, signing_key_password):
    # Set up the message
    msg = MIMEMultipart()
    msg['From'] = sender_email
    msg['To'] = recipient_email
    msg['Subject'] = subject

    # Add text body
    msg.attach(MIMEText(body, 'plain'))

    # Add attachments
    for attachment in attachments:
        with open(attachment['path'], 'rb') as f:
            file_data = f.read()
        attachment_part = MIMEApplication(file_data, Name=attachment['filename'])
        attachment_part['Content-Disposition'] = f'attachment; filename="{attachment["filename"]}"'
        msg.attach(attachment_part)

    # Sign and encrypt the message
    with open(signing_key_file, 'r') as f:
        signing_key_data = f.read()
    signing_key = crypto.load_privatekey(crypto.FILETYPE_PEM, signing_key_data, signing_key_password)
    p7 = crypto.SMIME.PKCS7()
    p7.set_flags(crypto.SMIME.PKCS7_DETACHED)
    p7.set_data(str(msg))
    p7.add_signer(crypto.SMIME.PKCS12.from_file(signing_key_file, signing_key_password).get_certificate(), signing_key, 'sha256')
    signed_data = p7.sign()

    with open(signing_key_file, 'r') as f:
        signing_key_data = f.read()
    signing_key = crypto.load_privatekey(crypto.FILETYPE_PEM, signing_key_data, signing_key_password)
    p7 = crypto.SMIME.PKCS7()
    p7.set_flags(crypto.SMIME.PKCS7_DETACHED)
    p7.set_data(signed_data)
    p7.add_certificate(crypto.X509.from_cryptography(signing_key.get_certificate()))
    p7.add_recipient(crypto.X509.from_cryptography(crypto.X509.from_cryptography(recipient_email)))
    encrypted_data = p7.encrypt()

    # Send the message
    with smtplib.SMTP('smtp.gmail.com', 587) as server:
        server.starttls()
        server.login(sender_email, 'password')
        server.sendmail(sender_email, recipient_email, encrypted_data.as_bytes())

# Example usage
sender_email = 'example@gmail.com'
recipient_email = 'recipient@example.com'
subject = 'Example email'
body = 'Hello,\n\nThis is an example email.\n\nRegards