我认为你说得对。
而且事实证明你不是第一个……在搜索 DISCOURSE_SMTP_PORT 465 时，我发现了一堆类似的问题。
- Not able to send email Net::ReadTimeout - #18 by Stranik
- Email not working but i can access smtp server from container
- DigitalOcean + Siteground Email via port 465 won’t work (2525 will work)
- Problem with SMTP configuration
- Post-install, Curl can send email, but Discourse cannot. Help to fix?
- Mail problem on discourse with reverse proxy
- Can't setup SMTP with SSL/TLS
- SMTP email issue Net::Timeout - #3 by neounix
最后一个包含一个（可能的？）解决方案链接。
有了这个补丁，就可以设置
DISCOURSE_SMTP_FORCE_TLS=true 来在端口 465 上使用隐式 TLS