无法通过SMTP发送电子邮件，因为“550-不允许中继”

import smtplib
from email.mime.text import MIMEText

# 邮件配置
smtp_server = 'smtp.example.com'
smtp_port = 587
username = 'your_username'
password = 'your_password'
from_addr = 'sender@example.com'
to_addr = 'receiver@example.com'
subject = 'Test Email'
content = 'This is a test email.'

# 创建邮件
msg = MIMEText(content)
msg['Subject'] = subject
msg['From'] = from_addr
msg['To'] = to_addr

# 发送邮件
try:
    server = smtplib.SMTP(smtp_server, smtp_port)
    server.starttls()
    server.login(username, password)
    server.sendmail(from_addr, to_addr, msg.as_string())
    server.quit()
    print('Email sent successfully!')
except smtplib.SMTPException as e:
    print(f'Error: {e}')