The “smuggled” SMTP MAIL/RCPT/DATA commands and header plus body text can be used to spoof an email message from any MAIL FROM address whose domain is hosted at email service A, to any RCPT TO address whose domain is hosted at email service B.
If I understand this correctly someone can use Microsoft/other commercial services to email a domain running postfix and make it comes from anyone on the initial service to anyone on the postfix domain. Nice. Good for targeted attacks and probably not bad to get some spam out.
Merry Christmas postfix.
Mailcow tracking bug, they claim the fix in the parent may cause the blocking of legimate traffic from incorrectly implemented smtp servers.