Flask博客站点Post请求后发送邮件失败问题排查

我在Flask搭建的博客站点中，希望用户提交Contact表单（POST请求完成后）自动发送邮件。表单提交的变量均能正常获取，但send_mail函数执行后，邮件始终无法送达收件箱。相关代码如下：

import smtplib
from flask import Flask, request, render_template

app = Flask(__name__)

def send_mail(who_will_receive: str, subject: str, message: str):
    """发送邮件给指定用户"""
    my_google_email = "email@gmail.com"
    password_google = "apppassword"  # 已替换为谷歌应用密码

    with smtplib.SMTP(host="smtp.gmail.com", port=587, timeout=120) as connection:
        connection.starttls()
        connection.login(user=my_google_email, password=password_google)
        connection.sendmail(
            from_addr=my_google_email,
            to_addrs=who_will_receive,
            msg=f"Subject: {subject}\n\n{message}".encode("utf8")
        )

@app.route("/contact", methods=["POST", "GET"])
def contact_page():
    if request.method == "POST":
        name = request.form['name']
        email = request.form['email']
        phone = request.form['phone']
        message = request.form['message']
        # 以下变量均能正常打印，说明表单数据获取正常
        print(name, email, phone, message)
        # 调用发送邮件函数，但邮件未送达
        send_mail("mymail@gmail.com", f"Contact from {name}", f"Name: {name}\nEmail: {email}\nPhone Number: {phone}\nMessage: {message}")
        return render_template("contact.html", form_submitted=True)
    return render_template("contact.html")

已尝试更换谷歌应用密码、为SMTP连接添加timeout=120参数，问题仍未解决。

• 检查垃圾邮件/促销文件夹：谷歌邮箱会自动过滤自动发送的邮件，先去垃圾箱、促销邮件目录查找是否有目标邮件。
• 补充邮件头部信息：当前邮件仅包含Subject字段，缺少From和To标识，容易被邮件服务器判定为垃圾邮件。修改邮件内容格式：

  msg = f"From: {my_google_email}\nTo: {who_will_receive}\nSubject: {subject}\n\n{message}".encode("utf8")
  

• 添加异常捕获排查错误：原代码未处理发送过程中的异常，可能存在隐性错误。修改send_mail函数，添加错误捕获与打印：

  def send_mail(who_will_receive: str, subject: str, message: str):
      my_google_email = "email@gmail.com"
      password_google = "apppassword"
      try:
          with smtplib.SMTP(host="smtp.gmail.com", port=587, timeout=120) as connection:
              connection.starttls()
              connection.login(user=my_google_email, password=password_google)
              msg = f"From: {my_google_email}\nTo: {who_will_receive}\nSubject: {subject}\n\n{message}".encode("utf8")
              connection.sendmail(from_addr=my_google_email, to_addrs=who_will_receive, msg=msg)
          print("邮件发送成功")
      except smtplib.SMTPException as e:
          print(f"SMTP发送错误：{str(e)}")
      except Exception as e:
          print(f"未知错误：{str(e)}")
  

• 确认谷歌账号配置：
  • 确保账号已开启两步验证，应用密码是在两步验证开启后生成的（未开启两步验证无法生成有效应用密码）。
  • 登录谷歌账号查看「最近活动」，确认SMTP登录是否被系统拦截，若有拦截提示，手动允许该设备/IP的登录请求。
• 切换SMTP连接方式：尝试使用SSL协议的465端口替代TLS的587端口：

  with smtplib.SMTP_SSL(host="smtp.gmail.com", port=465, timeout=120) as connection:
      connection.login(user=my_google_email, password=password_google)
      msg = f"From: {my_google_email}\nTo: {who_will_receive}\nSubject: {subject}\n\n{message}".encode("utf8")
      connection.sendmail(from_addr=my_google_email, to_addrs=who_will_receive, msg=msg)
  

• 验证收件人地址：确认send_mail中传入的收件地址"mymail@gmail.com"拼写完全正确，无大小写或字符错误。

内容的提问来源于stack exchange，提问作者lPitecus