| Abbreviation | Definition |
|---|---|
| MMP | Managed Mail Program |
| MMS | Manifest Mailing System |
| MN | Mongolia |
| MNR | Manor |
| MO | Macau |
| MO | Mail Order |
| MODS | Management Operating Data System |
| MOM | Military Ordinary Mail |
| MOPS | Mail Order Protection Scheme |
| MOS | Maintenance Operations Support Clerk |
| MP | Northern Mariana Islands |
| MPFSM | Multi-Position Flat Sorting Machine |
| MPLSM | Multi-Position Letter Sorting Machine |
| MPO | Military Post Office |
| MPO | Mobile Post Office |
| MPS | Mail Preference Service |
| MPSOM | Mail Processing Staffing Opportunity Model |
| MPTQM | Mail Preparation Total Quality Management |
| MPWCS | Mail Processing Work Credit System |
| MQ | Martinique |