Mail may be transported and "unloaded/sold" to designated mailboxes. Bring some water for your postal workers, and see how quickly they sort your mail.
After the mail has been delivered to a mailbox, pick up your paycheck!
Production of the LPS Post Office ~ Cost: $35,000 ~ Maintenance Cost: $12.50 per Day ~ Input: Water ~ Output: Mail
~ Location: Factories > Productions > Build Menu
Residential Mailboxes for LPS
~ Available Types: 10 ~ Cost: $25 ~ Daily Maintenance: 0 ~ Input: MAIL
~ Location: Productions > Selling Points > Build Menu
Price: $500; Daily Maintenance: $0; Location: Build Menu > Decorations > Decorations
LPS Postal Delivery Vehicle ~ Cost: $18,000 ~ Options: Mail, Diesel
Mail is automatically loaded in the back of the car (including loading mail animations).
~ Location: Cars > Drivables > Vehicle Menu

Thanks to Squigglze