FWIW, I've tried to understand this better, and have thrown together a quick test: https://github.com/hannob/smtpsmug https://github.com/hannob/smtpsmug This i

FWIW, I've tried to understand this better, and have thrown together a quick test: https://github.com/hannob/smtpsmug https://github.com/hannob/smtpsmug This is very much work in progress, and not documented yet. But it does detect the postfix issue.