We are experiencing the same problem; We're an IT company and our techs have looked into it after complaints from our customers about not receiving invoices.
The MYOB logo in emails sent from MYOB is myobb-email.png and is via a URL from files. pfs-payments-production. myob. com
This URL is flagged as a phishing url in microsoft hosted emails which means any clients using Microsoft will not be able to receive emails and they will all go to quarantine.
I sent a request off to support but they weren't able to help and I'm not sure where else I can escalate it to.