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.
After 6 months, it is true the check is considered stale dated but most banks will cash it anyway. You can request a stop payment on the check to ensure the check is returned if it is presented for payment, but also beware that most stop payment orders expire after one year and need to be renewed. No, a personal check is usually voided by a bank after 180 days.