Error encountered when sending emails in Misskey deployment via Docker

[jinghuashang]

ERR * [email] Error: Greeting never received {
e: Error: Greeting never received
at SMTPConnection._formatError (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:798:19)
at SMTPConnection._onError (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:784:20)
at Timeout. (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:718:22)
at listOnTimeout (node:internal/timers:581:17)
at process.processTimers (node:internal/timers:519:7) {
code: 'ETIMEDOUT',
command: 'CONN'
}
}
ERR * [api] Internal error occurred in admin/send-email: Greeting never received {
ep: 'admin/send-email',
ps: {
to: '@.com',
subject: 'Test email',
text: 'Yo',
i: '9pLgBR6XYI8h92Uj'
},
e: {
message: 'Greeting never received',
code: 'Error',
stack: 'Error: Greeting never received\n' +
' at SMTPConnection._formatError (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:798:19)\n' +
' at SMTPConnection._onError (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:784:20)\n' +
' at Timeout. (/misskey/node_modules/.pnpm/nodemailer@6.9.14/node_modules/nodemailer/lib/smtp-connection/index.js:718:22)\n' +
' at listOnTimeout (node:internal/timers:581:17)\n' +
' at process.processTimers (node:internal/timers:519:7)',
id: '74467ba1-ca92-45f3-a1b9-bbcb2487dfc9'
}
}

Misskey server located in China.

[CKylinMC]

Facing very similar issues, try telnet <SMTP_HOST> 25 (for non-ssl mode) and check if you can see 220 message from server.