I am a Systems Admin and am having issues with one of our clients Domains.
They are currently with a third party’s for their Domain management for their website and we have since changed them to Office 365 to manage their emails.
(We have done this many times with no issues btw)
Since changing them, they quite regularly receive bounce backs from other domains stating their mail is detected as spam (Bigpond, yahoo, gmail, some third party ones). The SPF, DKIM and DMARC are all functioning correctly. When sending a test email to us; upon checking the headers, DKIM = Pass, SPF = Pass, DMARC = Pass.
In the office 365 tenant, applicable domains and IP addresses have been added to the SPF record, spam filter options and Connection filter options.