Final answer:
Sensitive items like personal information and bills should be mailed using certified mail to ensure security and provide proof of mailing and delivery.
Step-by-step explanation:
Items containing handwriting or typewriting, personal information, bills, and statement accounts should be mailed using certified mail. Certified mail provides proof of mailing and delivery, which ensures that important documents such as personal communication, bills, and account statements are sent securely. When mailing sensitive information, it's crucial to choose a mail class that provides tracking and confirmation of delivery, which certified mail offers.