test_mail.py

#!/usr/bin/env python3
import argparse
import smtplib
import ssl
import dns.resolver  # Required for DNS lookup
from email.mime.text import MIMEText


def get_mx_record(domain):
    """
    Retrieve the highest priority MX record for the specified domain.
    """
    try:
        records = dns.resolver.resolve(domain, 'MX')
    except (dns.resolver.NoAnswer, dns.resolver.NXDOMAIN):
        print(f"No MX record found for domain {domain}")
        return None
    records = sorted(records, key=lambda record: record.preference)
    return str(records[0].exchange).rstrip('.')


def test_mail(
    smtp_server,
    smtp_port,
    smtp_user,
    smtp_password,
    from_email,
    to_email,
    subject="Test email",
    body="This is a test email",
    use_tls=True,
    certfile=None,
    keyfile=None,
    direct_send=False  # Flag for direct sending
):
    """
    Send a test email. If direct_send is enabled, it bypasses the specified SMTP server
    and sends the email directly to the recipient's domain SMTP server.
    """

    if direct_send:
        domain = to_email.split('@')[-1]
        mx_record = get_mx_record(domain)
        if mx_record is None:
            return  # Exit if we couldn't find an MX record
        smtp_server = mx_record

    # Setup the email message
    msg = MIMEText(body)
    msg["Subject"] = subject
    msg["From"] = from_email
    msg["To"] = to_email

    try:
        context = ssl.create_default_context()
        if certfile and keyfile:
            context.load_cert_chain(certfile=certfile, keyfile=keyfile)

        with smtplib.SMTP(smtp_server, smtp_port) as server:
            server.ehlo()  # It's good practice to identify ourselves to the SMTP server.

            # If we're not doing direct send or if we're using TLS, start the TLS session
            if use_tls or not direct_send:
                server.starttls(context=context)
                server.ehlo()  # Re-identify ourselves over the encrypted connection.

            if smtp_user and smtp_password and not direct_send:
                server.login(smtp_user, smtp_password)

            server.sendmail(from_email, [to_email], msg.as_string())

        print("Email sent successfully!")

    except Exception as e:
        print(f"Failed to send email. Error: {e}")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Send a test email.")
    parser.add_argument("from_email", help="The email address to send from.")
    parser.add_argument("to_email", help="The email address to send to.")
    parser.add_argument(
        "--smtp_server", help="The SMTP server address.", default="")
    parser.add_argument("--smtp_port", type=int,
                        help="The SMTP server port.", default=25)
    parser.add_argument(
        "--smtp_user", help="The SMTP server username.", default="")
    parser.add_argument("--smtp_password",
                        help="The SMTP server password.", default="")
    parser.add_argument("--subject", help="Email subject.",
                        default="Test email")
    parser.add_argument("--body", help="Email body.",
                        default="This is a test email.")
    parser.add_argument(
        "--use_tls", help="Use TLS for the SMTP connection.", action="store_true")
    parser.add_argument(
        "--certfile", help="Path to the client certificate file.", default="")
    parser.add_argument(
        "--keyfile", help="Path to the client key file.", default="")
    parser.add_argument(
        "--direct_send", help="Send email directly to the recipient's SMTP server based on MX lookup.", action="store_true")

    args = parser.parse_args()

    # If direct_send is active, use_tls is adapted to ensure compatibility with the recipient's server.
    use_tls = args.use_tls if not args.direct_send else True

    test_mail(
        args.smtp_server,
        args.smtp_port,
        args.smtp_user,
        args.smtp_password,
        args.from_email,
        args.to_email,
        args.subject,
        args.body,
        use_tls,
        args.certfile,
        args.keyfile,
        args.direct_send
    )