Outside suppliers are not receiving our Payment Advice Remittance Emails

Some time in early Jan 2023, we started receiving reports from some outside suppliers that they are not receiving our payment advice remittance emails. We have traced the entire process through PeopleSoft and all have transmitted successfully. However, suppliers still report that they are not receiving them from us. We had one supplier that reported the issue was on their end, and he had to "edit allowed and blocked sender and domains" in 365 Defender. Has anyone else experienced this and found that this solution fixed the issue? It's hard to troubleshoot this since this