Non-prior

• Why does a non-priority mail item come back/return to sender?
• How do I put the address on a non- priority letter?
• Where do I put the address on a non- priority letter?
• Where do I put a return address on a non-priority letter?
• What formats are allowed for a non- priority letter?
• What is the maximum weight for a non- priority letter? Standard vs non-standard mail format
• Are non-prior and prior allowed in the same mailbag?
• Is a handwritten address allowed on a non-prior letter?