There are extra services, that you can purchase for use with MEDIA MAIL, which provide additional protection and peace of mind.

Certificate of Mailing is your proof that you did mail the item.

Insuranced Mail provides protection while your item is in transit.

Delivery Confirmation provides confirmation that the item was delivered.  It provides the date and time of delivery or attempted delivery.

Signature Confirmation provide confirmation that the item was delivered.  It provides the date and time of delivery or attempted delivery and the name of the person who sign for the item.

Hint #1: CLERALY PRINTED LABELS are a must!

Hint #2: Enclose a packing slip, with your shipping address and return address, in case the address label somehow becomes unreadable.

Conclusion:  MEDIA MAIL is as safe as you make it!