Not receiving emails from addresses with a specific @ending

Title. I have a @live.com address.

I've checked my Outlook "rules," and none of them should be deleting emails from @blank addresses.

The sender has confirmed that the emails were "sent" on their end. They claim to not know why the emails have not been received.

I have checked Junk Mail.

I have seen an email from a @blank address successfully sent to someone else, and saw my email address listed as a CC. However I did not receive this CC.

I have tried disabling all of my rules in the unlikely case that they are deleting emails from @blank addresses, but am still waiting for a test email to be sent from a @blank address.

Could live mail/Outlook.com have any way of filtering emails besides the "rule" menu? Could it be something on the sender's end that they are unaware of?