Ubuntu服务器上Zoho Mail SMTP连接超时问题求助

我在Ubuntu服务器上使用Zoho Mail SMTP服务器发送邮件时遇到连接超时错误，但相同代码在Windows环境下可以正常执行。相关配置如下：

• 使用邮箱地址：mycustom_Email@example.com
• SMTP服务器：smtp.zoho.com
• SMTP端口：587

运行的Python代码如下：

from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from fastapi import FastAPI, HTTPException
from email.header import Header
from email.utils import formataddr
import smtplib  # 原代码遗漏此导入，已补充

sender_name= " Account Security"
smtp_server = "smtp.zoho.com"
smtp_port = 587
smtp_username = "########"
smtp_password = "PASSWORD" 

def send_reset_email(email, token, fullname):
    try:
        msg = MIMEMultipart()
        msg["From"] = formataddr((str(Header(sender_name, 'utf-8')), smtp_username))
        msg["To"] = email
        msg["Subject"] = "Password Reset Request"

        body = f"Dear {fullname},\n\n"
        body += "We received a request to reset your password. To proceed, please click the link below:\n\n"
        body += f"http://#####.com/reset-password?token={token}\n\n"
        body += "If you did not request this password reset, you can safely ignore this email. Your account security is important to us.\n\n"
        body += "Thank you for using our service!\n\n"
  
        msg.attach(MIMEText(body, "plain"))

        with smtplib.SMTP(smtp_server, smtp_port) as server:
            server.starttls()
            server.login(smtp_username, smtp_password)
            server.sendmail(smtp_username, email, msg.as_string())

    except Exception as e:
        raise HTTPException(status_code=500, detail="Failed to send reset email")

def send_verification_email(email, token):
    try:
        msg = MIMEMultipart()
        msg["From"] = smtp_username
        msg["To"] = email
        msg["Subject"] = "Email Verification Request"

        body = f"Dear User,\n\n"
        body += "We received a request to verify your email. To proceed, please click the link below:\n\n"
        body += f"https://########/verify_email/{token}\n\n"
        body += "If you did not request this email verification, you can safely ignore this email. Your account security is important to us.\n\n"
        body += "Thank you for using our service!\n\n"
    
        msg.attach(MIMEText(body, "plain"))

        with smtplib.SMTP(smtp_server, smtp_port) as server:
            server.starttls()
            server.login(smtp_username, smtp_password)
            server.sendmail(smtp_username, email, msg.as_string())
        print("Verification email sent successfully")
    except Exception as e:
        raise HTTPException(status_code=500, detail="Failed to send verification email")
    
print(send_verification_email("info@####.com","123456"))

排查与解决步骤 #

1. 测试网络连通性 #

先确认服务器能否访问Zoho的SMTP端口：

• 执行telnet测试：telnet smtp.zoho.com 587
• 或使用nc命令：nc -zv smtp.zoho.com 587
  如果连接失败，说明服务器防火墙/安全组限制了587端口的出站流量，需要开放。

2. 调整防火墙规则 #

• Ubuntu默认使用ufw，开放587端口：sudo ufw allow out 587/tcp
• 若使用云服务器，需同步在云平台安全组中添加出站方向的TCP 587端口允许规则。

3. 增加SMTP连接超时 #

在代码中手动设置更长的超时时间，避免默认超时过短：

with smtplib.SMTP(smtp_server, smtp_port, timeout=30) as server:
    server.starttls()
    # 后续代码保持不变

4. 检查Zoho账户设置 #

• 确认Zoho邮箱已启用SMTP服务（进入邮箱设置→"Mail Accounts"→"Outgoing Server (SMTP)"开启）
• 若账户开启了两步验证，需使用应用专用密码代替原账户密码登录SMTP。

5. 验证DNS解析 #

确认服务器能正确解析Zoho的SMTP域名：
执行nslookup smtp.zoho.com，若解析异常，可更换DNS服务器（如改为8.8.8.8）。

6. 尝试SSL直连 #

若587端口的STARTTLS方式仍有问题，可改用465端口的SSL连接：
修改代码中的SMTP类为SMTP_SSL，端口改为465：

with smtplib.SMTP_SSL(smtp_server, 465) as server:
    server.login(smtp_username, smtp_password)
    # 后续代码保持不变

同时确保服务器开放465端口的出站流量。

内容的提问来源于stack exchange，提问作者Yahya Al Hattali