Good Morning Naret,
Here are the findings and recommendation:
Spam blocker is not configured for any Carlson Rezidor hotels including yours.
If email was affected by a firmware upgrade (which has never happened before) no email would come through at all.
You would need to add the sender into the contacts for the sales mailbox and ensure it is not being blocked by their anti-virus or anti-spam applications.
If still an issue, please reach out to the sender; advise them to provide us with the Delivery Notification.
Please check in the Sales’s JUNK Mail folder if the emails are automatically moved there.
Queries, let us know.