使用smtplib发送带主题邮件触发SMTPSenderRefused(555)错误求助

错误根源 #

你遇到的SMTP SenderRefused (555)错误，核心是**smtplib.SMTP.sendmail的参数使用错误**。这个方法的第三个参数必须是完整的邮件文本（包含邮件头和正文），而不是把主题、内容分开传递。你现在的写法会让SMTP服务器收到格式完全不符合规范的邮件内容，触发语法错误。

另外代码里还有个小语法错误：server.login("email@email.com", "Email_PW"])多了一个闭合方括号，需要去掉。

正确发送带主题的邮件 #

不需要去掉主题，只要按照SMTP规范构造完整的邮件内容即可，下面是两种可行的实现方式：

方式1：手动构造邮件内容（简单直接） #

直接拼接符合邮件格式的字符串，包含From、To、Subject等头信息，正文与头信息用空行分隔：

@views.route('/thank-you', methods=['POST'])
def thank_you():
    subject = request.form.get("subject")
    first_name = request.form.get("first_name")
    last_name = request.form.get("last_name")
    email = request.form.get("email")
    message = request.form.get("message")

    response_message = "Thank you for contacting me."

    # 初始化SMTP服务器
    server = smtplib.SMTP("smtp.gmail.com", 587)
    server.starttls()
    server.login("email@email.com", "Email_PW")  # 修正多余的方括号

    # 构造给用户的回复邮件
    msg_to_user = f"""From: Your Name <email@email.com>
To: {first_name} <{email}>
Subject: {subject}

{response_message}
"""
    server.sendmail("email@email.com", email, msg_to_user)

    # 构造给自己的通知邮件
    msg_to_self = f"""From: {first_name} <{email}>
To: Your Name <email@email.com>
Subject: New Contact Form Submission - {subject}

First Name: {first_name}
Last Name: {last_name}
Sender Email: {email}
Message: {message}
"""
    server.sendmail("email@email.com", "email@email.com", msg_to_self)

    # 关闭连接（好习惯）
    server.quit()

    title = "Thank You"
    return render_template('thank_you.html', title=title, subject=subject, first_name=first_name, last_name=last_name, email=email, message=message)

方式2：使用email模块（更规范，支持复杂格式） #

如果需要处理中文、特殊字符或者后续扩展HTML邮件，推荐用Python内置的email模块构造邮件，避免手动拼接的格式问题：

from email.mime.text import MIMEText
from email.header import Header

@views.route('/thank-you', methods=['POST'])
def thank_you():
    subject = request.form.get("subject")
    first_name = request.form.get("first_name")
    last_name = request.form.get("last_name")
    email = request.form.get("email")
    message = request.form.get("message")

    response_message = "Thank you for contacting me."

    server = smtplib.SMTP("smtp.gmail.com", 587)
    server.starttls()
    server.login("email@email.com", "Email_PW")

    # 构造给用户的邮件
    msg_user = MIMEText(response_message, 'plain', 'utf-8')
    msg_user['From'] = Header("Your Name <email@email.com>", 'utf-8')
    msg_user['To'] = Header(f"{first_name} <{email}>", 'utf-8')
    msg_user['Subject'] = Header(subject, 'utf-8')
    server.sendmail("email@email.com", email, msg_user.as_string())

    # 构造给自己的邮件
    self_content = f"""First Name: {first_name}
Last Name: {last_name}
Sender Email: {email}
Message: {message}"""
    msg_self = MIMEText(self_content, 'plain', 'utf-8')
    msg_self['From'] = Header(f"{first_name} <{email}>", 'utf-8')
    msg_self['To'] = Header("Your Name <email@email.com>", 'utf-8')
    msg_self['Subject'] = Header(f"New Contact Form Submission - {subject}", 'utf-8')
    server.sendmail("email@email.com", "email@email.com", msg_self.as_string())

    server.quit()

    title = "Thank You"
    return render_template('thank_you.html', title=title, subject=subject, first_name=first_name, last_name=last_name, email=email, message=message)

额外提示 #

你的HTML表单里的<select>标签写法有小问题，默认提示文本应该放在一个disabled selected的<option>里，否则部分浏览器会显示异常：

<select name="subject" id="subject">
    <option disabled selected>What is this message about?</option>
    <option value="Bible">Bible</option>
    <option value="Spiritual Things">Spiritual Things</option>
    <option value="Website">Website</option>
    <option value="Just to Talk">Just to talk</option>
    <option value="Other">Other</option>
</select>

内容的提问来源于stack exchange，提问作者Dustin916