A mail sack or mailsack is a mail bag used to carry large quantities of mail. Different handling and security requirements for different classes of mail is integral to the postal rate structure. A mail sack is not a locked bag since they need little security. In contrast to a similar mailbag — referred to as a mail pouch (for more sensitive mail such as personal letters and military mail) that employs a locking mechanism on the top of the bag. A mail pouch has special closely spaced eyelets and a strong strap to secure the top where access into the bag is closed off and locked, where a mail sack has none of these features.