我不知道SMTP服务出了什么问题

[satonotdead]

您需要检查安全选项，因为它不是很精确，您需要将其关闭（同时不影响您的安全性）。

Setting up SMTP

If you want to disable TLS, you need to uncomment this line, and set it to false: #DISCOURSE_SMTP_ENABLE_START_TLS: true # (optional, default true) However, there’s no relationship between POODLE and newer TLS protocol versions, nor is there any relationship between SMTP and POP3. Mailgun does support TLS on SMTP connections, they just don’t support it correctly.