Python调用smtplib.SMTP连接Gmail服务器时程序冻结问题求助

Hey there! It’s super frustrating when your script freezes mid-execution, especially before even getting to the authentication step. Let’s break down the possible causes and practical fixes for this issue.

First, Try This Modified Script #

Adding a timeout to your SMTP connection and basic error handling will help you diagnose the problem immediately instead of waiting indefinitely:

import smtplib
from socket import timeout

fromaddr = 'XXX@gmail.com'
toaddrs = 'YYY@gmail.com'
msg = 'Enter your message here'
username = 'XXX@gmail.com'
password = 'PPP'

try:
    # Add a 10-second timeout to prevent infinite freezing
    server = smtplib.SMTP('smtp.gmail.com', 587, timeout=10)
    print("Connected to SMTP server successfully!")
    server.starttls()
    server.login(username, password)
    server.sendmail(fromaddr, toaddrs, msg)
    print("Email sent!")
    server.quit()
except timeout:
    print("Connection timed out! Check your network or SMTP settings.")
except Exception as e:
    print(f"An error occurred: {str(e)}")

Common Causes & Fixes #

1. Network Restrictions (Firewall/Proxy/ISP Block) #

The most likely culprit is a network issue blocking outgoing connections to port 587:

• Check your local firewall: Ensure Windows Defender Firewall, macOS Firewall, or any third-party firewall isn’t blocking Python from accessing the internet.
• Proxy configuration: If you’re behind a corporate or school proxy, you’ll need to configure smtplib to use it. You can add a proxy handler before creating the SMTP connection.
• ISP port blocking: Some ISPs block port 587 for anti-spam reasons. Try switching to port 465 (SMTP_SSL) instead—note you won’t need server.starttls() when using this method:

  server = smtplib.SMTP_SSL('smtp.gmail.com', 465, timeout=10)
  

2. Missing Timeout in Older smtplib (Pre-Python 3.7) #

Python 3.6’s smtplib.SMTP doesn’t set a default timeout. If the connection can’t be established, it’ll hang forever. Adding the timeout parameter (like in the modified script) forces it to fail fast, giving you a clear error message instead of freezing.

3. Gmail Server Access Restrictions #

Even before the login step, Gmail’s servers might throttle or block connections from unfamiliar IPs:

• If you have 2FA enabled on your Gmail account, use an App Password instead of your regular password (this is more secure than enabling "Less secure app access").
• Check your Gmail account’s Security Log to see if the connection attempt was flagged as suspicious.

Final Notes #

Always include error handling in your scripts to catch issues early, and consider upgrading to a newer Python version (3.7+)—they have better default timeouts and improved smtplib functionality.

内容的提问来源于stack exchange，提问作者OD1995