The affected email, bookingonline@itcbangkok.com, does not belong to Carlson or Radisson.
If you are saying that the affected email address received a bounce-back message when sending mails to Sales team, would it be possible for them to send the screenshot to your email address?
Did it get the same bounce back error when sending an email to you?
What was the error message: have you googled it for resolution?
Which Sales email address that it was sending to?