邮件无法发送问题排查及Python邮件发送代码错误分析请求

Hey there, let's tackle your two email sending problems one by one:

一、Troubleshooting "Email Won't Send" General Issues #

If your email isn't going through, start checking these common culprits:

• Incorrect SMTP Config: Double-check the SMTP server address and port (e.g., Gmail uses smtp.gmail.com:587, Outlook uses smtp.office365.com:587). Make sure TLS/SSL is enabled as required.
• Authentication Failures: Verify your sender email and password are correct. For Gmail specifically:
  • If you have 2-step verification enabled, you need to use an App Password instead of your regular account password.
  • The "Less secure apps" option is mostly deprecated now, so App Passwords are the recommended approach.
• Network Blockages: Check if your firewall, antivirus, or proxy is blocking the SMTP port (usually 587 or 465). Try pinging the SMTP server to confirm basic connectivity.
• Invalid Email Format: SMTP requires proper email headers (like From, To, Subject) and a blank line between headers and body. Missing these can get your message rejected by the server.
• Recipient/Sender Restrictions: Ensure the recipient email exists and hasn't blocked you. Also, check if your sender account has hit a daily sending limit (common with free email services).

二、Fixing the Python Code That Always Outputs "Email not sent" #

Let's break down the issues in your code and fix them:

1. Overly Broad & Risky Exception Handling #

Your except: catches every possible error but gives zero context about what went wrong. Even worse, if an error happens before the server variable is initialized (like a failed connection), calling server.quit() later will throw another error because server doesn't exist yet.

2. Non-Standard Email Format #

You're sending raw text as the message, but SMTP expects a properly formatted email with mandatory headers. Without From, To, and Subject fields, most mail servers will reject the message outright.

3. Gmail-Specific Authentication Limits #

As mentioned earlier, Gmail no longer allows regular passwords for SMTP login if 2-step verification is enabled. You need an App Password to authenticate successfully.

Corrected Code Example #

import smtplib
from email.mime.text import MIMEText

port = 587
sender_mail = input("Enter your email address : ")
# Note: Gmail users with 2FA enabled must use an App Password here
sender_password = input("Enter your password : ")
receiver_mail = input("Enter receiver's mail address : ")
subject = input("Enter email subject : ")
message_body = input("Enter the message you want to send : ")

# Build a standards-compliant email message
msg = MIMEText(message_body)
msg['From'] = sender_mail
msg['To'] = receiver_mail
msg['Subject'] = subject

try:
    server = smtplib.SMTP("smtp.gmail.com", port)
    server.starttls()  # Enable TLS encryption for security
    server.login(sender_mail, sender_password)
    # Send the formatted MIME message instead of raw text
    server.send_message(msg)
    print("Email sent successfully")
except Exception as e:
    # Print exact error details to diagnose the problem
    print(f"Email not sent. Error details: {str(e)}")
finally:
    # Ensure we close the server connection even if an error occurs
    if 'server' in locals():
        server.quit()

Key Fixes Explained #

• Used email.mime.text.MIMEText to create a properly structured email with all required headers.
• Added specific exception handling to print error details—critical for debugging why the send failed.
• Used a finally block to safely close the SMTP connection, avoiding resource leaks.
• Added a subject input to make the email fully functional and compliant with mail server requirements.

内容的提问来源于stack exchange，提问作者Mayank Goel