Once you reserve a PO Box at the Post Office location, link it to your USPS.com account. You can manage it online instead of the Post Office location. Link a PO Box to an USPS.com Account
Quick Answer. Cashier's checks themselves do not expire as personal checks do. However, the funds behind the check are subject to state escheat laws.
Discovering an unredeemed check might seem like found money until you consider its expiration date. While some U.S. checks state how long you have to cash them on the check itself, others typically expire in a set number of days after being written. Not only does this encourage responsibility on the part of the check's recipient, it protects the issuer from overdrafts due to lack of funds if a recipient fails to redeem the check before it expires.