International Parcel Not Found, Emails to Cust Service Bounce Back

Trying to track my International Parcel that was supposed to arrive a month ago from USA, Tracking no is UM ********** 55US. SAPO tracking does not list this parcel, and when I send an email to customer services ********** to get an update, it bounces back with :

********** host inbound-smtp.eu-west-1.amazonaws.com [54.239.39.100] SMTP error from remote mail server after RCPT ********** 550 5.1.1 Requested action not taken: mailbox unavailable