Python Code Example for mySMTP with smtplib

Python’s built-in smtplib module lets you send email through mySMTP without installing third-party packages. You can use STARTTLS on port 587 or implicit TLS on port 465 (Python’s SMTP_SSL class, which negotiates TLS despite its name).

Prerequisites

Python 3.8 or later
Your mySMTP username and password from the setup email
Your mySMTP hostname from the setup email (shown as relayxx.mysmtp.com in these examples)

STARTTLS on port 587 (recommended)

import os
import smtplib
from email.message import EmailMessage

SMTP_HOST = os.getenv('MYSMTP_HOST', 'relayxx.mysmtp.com')
SMTP_USER = os.getenv('MYSMTP_USER')
SMTP_PASS = os.getenv('MYSMTP_PASS')

msg = EmailMessage()
msg['From'] = 'you@yourdomain.com'
msg['To'] = 'recipient@example.com'
msg['Subject'] = 'Test email from Python'
msg.set_content('This is a plain text test message sent through mySMTP.')

with smtplib.SMTP(SMTP_HOST, 587) as server:
    server.starttls()
    server.login(SMTP_USER, SMTP_PASS)
    server.send_message(msg)

print('Message sent successfully')

Replace relayxx.mysmtp.com with your real hostname from the mySMTP setup email. Load credentials from environment variables, never hardcode them in source files.

Implicit TLS on port 465

If your network blocks port 587, use implicit TLS on port 465:

import os
import smtplib
from email.message import EmailMessage

SMTP_HOST = os.getenv('MYSMTP_HOST', 'relayxx.mysmtp.com')
SMTP_USER = os.getenv('MYSMTP_USER')
SMTP_PASS = os.getenv('MYSMTP_PASS')

msg = EmailMessage()
msg['From'] = 'you@yourdomain.com'
msg['To'] = 'recipient@example.com'
msg['Subject'] = 'Test email from Python'
msg.set_content('This is a plain text test message sent through mySMTP.')

with smtplib.SMTP_SSL(SMTP_HOST, 465) as server:
    server.login(SMTP_USER, SMTP_PASS)
    server.send_message(msg)

print('Message sent successfully')

HTML body with attachment

import os
import smtplib
from email.message import EmailMessage
from email.utils import make_msgid
import mimetypes

SMTP_HOST = os.getenv('MYSMTP_HOST', 'relayxx.mysmtp.com')
SMTP_USER = os.getenv('MYSMTP_USER')
SMTP_PASS = os.getenv('MYSMTP_PASS')

msg = EmailMessage()
msg['From'] = 'you@yourdomain.com'
msg['To'] = 'recipient@example.com'
msg['Subject'] = 'HTML email with attachment'

msg.set_content('This is the plain text fallback.')
msg.add_alternative(
    '<h1>Hello</h1><p>This is an HTML message.</p>',
    subtype='html'
)

filepath = '/path/to/invoice.pdf'
ctype, encoding = mimetypes.guess_type(filepath)
if ctype is None or encoding is not None:
    ctype = 'application/octet-stream'
maintype, subtype = ctype.split('/', 1)

with open(filepath, 'rb') as fp:
    msg.add_attachment(
        fp.read(),
        maintype=maintype,
        subtype=subtype,
        filename='invoice.pdf'
    )

with smtplib.SMTP(SMTP_HOST, 587) as server:
    server.starttls()
    server.login(SMTP_USER, SMTP_PASS)
    server.send_message(msg)

print('Message sent successfully')

Common errors

535 Authentication failed

Your username or password is incorrect, or your account is not yet activated. Re-enter credentials exactly as shown in the setup email. See Setting up SMTP credentials.

Connection timeout or refused

Your network or host may block port 587. Try port 2525 with STARTTLS, or port 465 with SMTP_SSL (implicit TLS). See Supported SMTP ports and encryption.

TLS handshake failure

The encryption method does not match the port. Use starttls() for ports 587 and 2525. Use SMTP_SSL for port 465.

Test your SPF, DKIM, and DMARC setup with the mySMTP Deliverability Toolbox before sending large volumes.

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Python Code Example for mySMTP with smtplib

Prerequisites

STARTTLS on port 587 (recommended)

HTML body with attachment

Common errors

​Prerequisites

​STARTTLS on port 587 (recommended)

​HTML body with attachment

​Common errors

​Related articles

Prerequisites

STARTTLS on port 587 (recommended)

HTML body with attachment

Common errors

Related articles