当我从“发送一封简短的电子邮件时[电子邮件保护]“或任何其他电子邮件 acc，该消息在 Gmail、hotmail 等的收件箱中接收良好，但如果我再次发送长文本消息，电子邮件就会退回并显示错误：
<[email protected]>: host gmail-smtp-in.l.google.com[xx.xx.153.27] said:
550-5.7.1 [xx.xx.xx.167 12] Gmail has detected that this message is
550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to
Gmail, 550-5.7.1 this message has been blocked. Please visit 550-5.7.1
https://support.google.com/mail/?p=UnsolicitedMessageError for more 550
5.7.1 information. gz13-20020a170906f2cd00b00a0e79089b8fsi528438ejb.874 -
gsmtp (in reply to end of DATA command)
附言：SPF 和 DMARC 设置良好，mail-tester.com 的邮件评分测试为 10/10
收到的消息示例：
title: hi
body : hi
未收到消息的示例：
title : hi
body : Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris pellentesque auctor consectetur. Phasellus quis ipsum consequat, ultrices est eget, mollis magna. Maecenas porttitor enim vel laoreet vestibulum. Phasellus tincidunt mi in erat efficitur, a maximus est vestibulum. Etiam faucibus purus quis euismod accumsan. Vestibulum placerat mollis erat vitae elementum. Sed id lacinia augue. Sed venenatis, tellus in elementum mollis, eros diam maximus arcu, eu bibendum risus justo ac nunc. Phasellus suscipit ex et augue ultricies, mollis tincidunt est consequat. Morbi id sollicitudin purus, sed consequat orci. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia curae; Sed tincidunt nunc et pretium fringilla. Suspendisse sollicitudin, lectus nec fringilla iaculis, metus turpis maximus massa, vitae elementum tellus nisl eleifend massa. Morbi finibus, velit nec eleifend maximus, nisl nunc elementum diam, hendrerit porttitor nisl ipsum at purus. Integer convallis rhoncus dolor ac condimentum. Sed suscipit vitae tellus eget gravida.
我正在通过（Vertiualmin）从 Usermin 面板发送电子邮件。
为什么我的服务器没有发送长消息？
答案1
https://support.google.com/mail/answer/81126?hl=en#zippy=%2Crequirements-for-all-senders
总之，Gmail 需要
SPF、DKIM 和 DMARC 您的发送 IP 地址必须具有 PTR 记录。
根据互联网格式标准 (RFC 5322) 格式化消息。
如果您的消息是 HTML 格式，请按照 HTML 标准进行格式化
使用 TLS 连接传输电子邮件。