Flask-Mail无法发送邮件：连接拒绝与内部服务器异常求助

我正在开发一款Web应用，通过HTML表单获取用户邮箱地址后发送一次性验证码（OTP），用于网站后续访问验证：

• 模板文件夹中有两个HTML文件，分别用于收集用户邮箱和输入OTP；
• 通过config.json文件存储发送OTP的账号ID和密码。

from flask import Flask, render_template, request
from random import randint
import json
from flask_mail import *

with open('config.json','r') as f:
    params = json.load(f)['params']
mail = Mail(app)

otp = randint(100,999)      #otp production

app.config['MAIL_SERVER'] = 'smtp.gmail.com'
app.config['MAIL_PORT'] = 465
app.config['MAIL_USE_TLS'] = False
app.config['MAIL_USE_SSL'] = True
app.config['MAIL_USERNAME'] = params['gmail-user']
app.config['MAIL_PASSWORD'] = params['gmail-password']


@app.route('/')
def home():
    return(render_template('otpgive.html'))

@app.route('/getOTP', methods = ['POST'])
def getOTP(): #OTP send and Verify here
    email_id = request.form['usermail']
    msg = Message('OTP for the APPLICATION', sender = 'my_email', recipients = [email_id]) 

  #my_email is the email through which i plan to send messages.

    msg.body = "Greetings! Your email has been verified successfully. Kindly note your OTP is " + str(otp)
    mail.send(msg)
    return render_template('otpconfirm.html')

@app.route('/validateOTP', methods = ['POST'])
def validateOTP():
    userotp = request.form['otp']
    if (otp == int(userotp)):
        return ("Email Verified Succcessfully ")
    else:
        return render_template('otpgive.html',msg = 'incorrect otp')

if __name__ == '__main__':
    app.run(debug = False)
    #app.run(host='0.0.0.0',port=5000, debug = True)

• 关闭防火墙；
• 设置端口为0.0.0.0；
• 设置debug = False。

预期应用能成功向用户发送邮件，但实际出现以下错误：

Internal Server Error
服务器遇到内部错误，无法完成您的请求。可能是服务器过载或应用存在错误。

ConnectionRefusedError:
[WinError 10061] 由于目标计算机积极拒绝，无法连接。

1. 修复代码初始化顺序 #

代码中先初始化mail = Mail(app)，但此时Flask应用实例app还未创建，邮箱配置也未加载，这是导致内部错误的直接原因。正确顺序如下：

from flask import Flask, render_template, request
from random import randint
import json
from flask_mail import Mail, Message

# 1. 先创建Flask应用实例
app = Flask(__name__)

# 2. 加载配置并设置邮箱参数
with open('config.json','r') as f:
    params = json.load(f)['params']

app.config['MAIL_SERVER'] = 'smtp.gmail.com'
app.config['MAIL_PORT'] = 465
app.config['MAIL_USE_TLS'] = False
app.config['MAIL_USE_SSL'] = True
app.config['MAIL_USERNAME'] = params['gmail-user']
app.config['MAIL_PASSWORD'] = params['gmail-password']

# 3. 最后初始化Mail对象
mail = Mail(app)

2. 解决Gmail SMTP连接拒绝问题 #

Gmail默认拦截第三方应用登录，需做以下配置：

• 启用应用专用密码：若账号开启了两步验证，需在Google账号安全设置中生成应用专用密码，替换config.json中的密码；
• 切换SMTP端口：尝试使用TLS端口587，对应修改配置：MAIL_PORT = 587、MAIL_USE_TLS = True、MAIL_USE_SSL = False；
• 检查账号权限：确保Google账号未限制SMTP服务访问。

3. 修复OTP全局变量问题 #

当前OTP是全局变量，多用户同时请求会导致验证码被覆盖，建议将OTP存储在用户会话中：

from flask import session

@app.route('/getOTP', methods = ['POST'])
def getOTP():
    email_id = request.form['usermail']
    otp = randint(1000,9999)  # 建议使用4位OTP提升安全性
    session['otp'] = otp
    # 发件人需替换为实际的Gmail账号
    msg = Message('应用验证OTP', sender=params['gmail-user'], recipients=[email_id])
    msg.body = f"您好！您的邮箱验证验证码是：{otp}"
    mail.send(msg)
    return render_template('otpconfirm.html')

@app.route('/validateOTP', methods = ['POST'])
def validateOTP():
    userotp = request.form['otp']
    if session.get('otp') == int(userotp):
        session.pop('otp')  # 验证成功后清除会话中的OTP
        return "邮箱验证成功！"
    else:
        return render_template('otpgive.html', msg='验证码错误，请重新获取')

4. 修正发件人地址 #

代码中sender = 'my_email'需替换为实际的发件邮箱（即params['gmail-user']），否则邮件服务会拒绝发送请求。

内容的提问来源于stack exchange，提问作者HS077