Hi Grinderb,
I'd like to confirm that you can't receive emails and the sender who sent emails to you received the error "550 #5.1.0 Address rejected". In order to narrow down the issue, I'd like to collect some information:
1. Do you mean that you can't receive any emails from external users or only can't receive emails from some specific senders?
2. Can other users in your organization receive emails?
I've checked the domain you provided above, the MX record and SPF record is correct. I suggest you use a Hotmail account to send a test email to your Office 365 account and another Office 365 account in your organization and check if the email can be received. Any updates, feel free to let me know.
@Patrick, thanks for your information.
Thanks,
Aaron Yuan