A 'proscribed alias' is an alias which used to belong to another Pobox account. In order to prevent confusion on the part of both message senders and recipients, we restrict people from using recently used addresses for 30 days.
During that 30 day period, people who are attempting to contact the person who used to have the account will receive a bounce message. By this method, we hope to prevent a flood of misdirected mail when someone new chooses the address.
If you are seeing this message because you are trying to move an address between two accounts you own, please contact Customer Support. For help on moving an alias to a different account, follow the steps on this page.