I tried SMTP communication with Python

I had an opportunity to implement SMTP communication in Python, so I will write the implementation method.

When I was researching various implementation methods, I found a lot of information about implementing with the legacy API of the standard library, but I could not find much method with the currently recommended API. Django, a web framework, also uses legacy APIs, so I couldn't refer to the code of major libraries and frameworks. So, I implemented it while reading the code centering on the Python smtplib and ʻemail` standard libraries.

environment

• OS: MacOS Catalina
• Python: 3.7
• Library: smtplib, email (Python standard libraries)

Implementation details

1. Establishing a connection with the SMTP server
2. SMTP Auth
3. Send email content
4. Log the destinations that failed when sending to multiple destinations

Source code

import smtplib
from email.message import EmailMessage

class MailClient:
    def __init__(self, mail_data: Dict[str, Any] = {}) -> None:
        """
        Args:
            mail_data(Dict[]): Defaults to {}.
        """

        self._mail_data = mail_data

    def request(self) -> bool:
        """
        Returns:
            bool
        """

        with smtplib.SMTP(host=SMTP_HOST, port=int(SMTP_PORT)) as smtp:
            smtp.login(SMTP_USER, SMTP_PASSWORD)
            errors = smtp.send_message(self.message())

            if isinstance(errors, dict) and len(errors) > 0:
                logger.warn(
                    f'''Failed to send to all recipients.
                    Details: {errors}'''
                )

        return True

    def message(self) -> EmailMessage:
        msg = EmailMessage()
        msg['From'] = self._mail_data['from_address']
        msg['To'] = self._mail_data['to_address']
        msg['Subject'] = self._mail_data['subject']
        msg.set_default_type('text/plain')
        msg.set_content(self._mail_data['message'])

        bcc = self._mail_data.get('bcc')
        if bcc:
            msg['Bcc'] = convert_to_str(bcc)

        cc = self._mail_data.get('cc')
        if cc:
            msg['Cc'] = convert_to_str(cc)

        return msg

Commentary

request method

Start a connection with the SMTP server with smtplib.SMTP. If you are using TLS, use smtplib.SMTP_SSL, or make a connection in clear text and then usestarttls ()to connect with TLS. After successfully establishing the connection, authenticate with login (). Then send the data with send_message. It is sendmail that is actually responsible for sending data. Execute the SMTP command in this function to send an email. Regarding error handling, this time I didn't write try-except because I can simply raise if an exception occurs. However, when sending to multiple destinations, if even one fails, it is recorded as a log. That information is the return value of send_message and is stored in the ʻerrors` variable. The error type is Dict, the key is the destination address, and the value is a tuple containing the STMP response code and the corresponding message. If you want to know more about when send_message / sendmail returns a value, go to here There is a source code, so please read it.

message method

This time, the mail data is created using EmailMessage of the email module, but you can directly assign a character string to send_message or sendmail. However, we do not recommend it because it is difficult if you do not understand the protocol specifications. Use Email Message whenever possible.

in conclusion

I was planning to publish this article sooner, but I forgot to write it halfway, so it became like writing a blog (laughs). Have a nice year: snowman2:

Reference material

--smtplib --- SMTP Protocol Client

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