使用smtplib发送邮件遇SMTPNotSupportedError，求解决方案

Hey there, let's break down what's happening here and fix that error!

The Root Cause #

Your error SMTPNotSupportedError: STARTTLS extension not supported by server means exactly what it says: the MailEnable SMTP server you're connecting to doesn't support the STARTTLS encryption protocol. When you call server.starttls(), the server doesn't recognize that command, hence the crash.

Step-by-Step Fix #

Here's how to adjust your code to work with your server:

• Remove the starttls() call: Since your server doesn't support this encryption method, we can skip this step entirely.
• Simplify the server connection: You're currently initializing the SMTP server and then calling connect() separately—we can combine these into one line to clean things up.
• Verify server settings: Double-check that your SMTP address ('mailenable') and port (25) are correct for your MailEnable instance (25 is the standard unencrypted SMTP port).

Modified Working Code #

import smtplib
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.base import MIMEBase
from email import encoders

toaddr = "mailto@mail.com"
head = "TRY"
body = "XxX"
fromaddr = "mailsender@mail.com"

msg = MIMEMultipart()
msg['From'] = fromaddr
msg['To'] = toaddr
msg['Subject'] = head
password = "password"

msg.attach(MIMEText(body, 'plain'))

# Combine initialization and connection into one line
server = smtplib.SMTP('mailenable', 25)
# Removed server.starttls() since it's not supported
server.ehlo() # This is usually optional but harmless
server.login(fromaddr, password)
text = msg.as_string()
server.sendmail(fromaddr, toaddr, text)
server.quit()

Additional Troubleshooting Tips #

• If you still get login errors, check if your MailEnable server allows plain-text authentication (since we're not using encryption here). You might need to adjust the server's security settings to permit this.
• If your server does support encryption but on a different port:
  • For STARTTLS on port 587: Use smtplib.SMTP('mailenable', 587) and re-add server.starttls() (only if the server actually supports it on this port).
  • For SSL encryption on port 465: Use smtplib.SMTP_SSL('mailenable', 465) instead of smtplib.SMTP() (no need for starttls() in this case).

内容的提问来源于stack exchange，提问作者Mert Türkyılmaz