Certified mail must be addressed for domestic delivery. It can not be used for international mail. Registered Mail Registered mail is the most secure service the Post Office provides. Through a system of receipts, registered mail is monitored from its insertion into the mail system to its destination. Because registered mail is separated from first class mail for the extra security, it can be delayed one or two days beyond the normal delivery times.
Registered mail is accepted for international mail deliveries.
Insured Mail Insured mail provides indemnity for lost damaged or riffled articles. To be insured articles must have a value and have proof of value. The articles must be properly packaged as an insurable item before the clerk will accept it. Tips for Better Service Mail Early. Prepare as much of the paper work as possible before entering the line.