I've bene working on this issue for around 2+ months now and have been back and forth with Google workspace support and gotten nowhere. I'm wondering if anyone else has had any luck with this specific issue or has contact with the right people that can help?
The public thread I made about this is here: https://support.google.com/mail/thread/207539747?hl=en
Essentially; Google rejects legitimate mail from Office365 senders due to the IPv6 ranges they're sent from when they're valid senders. If the mail is sent from the same domain via another source & IPv4 they're immediately accepted.
During our testing we found an obscure issue where replacing the SPF to break the returned IP ranges as so: include:spf.protection.outlook.com to a:spf.protection.outlook.com - this caused Google to accept the mail immediately into inbox & not issue a bounce-back. - Google fixed this workaround once we brought it to their attention, this work-around no longer works.
LinkedIn
Twitter
