Qualifications for personnel selected to attend the postal school are found in DoD 4525.6-M, para C5.3. Service specific requirements can be found in DA PAM 611-21, and OPNAV 5112.6c. Students who meet the criteria may be enrolled in the school, and upon completion, will receive the following action:
Army – Soldiers will receive the Additional Skill Identifier (ASI) F5 for completing the Postal Operations Course and ASI F4 for completing the Postal Supervisor Course.
You should talk to someone at your school house. When I was there for school they were looking for volunteers.BUt that was 8 yeras ago. Being a 42A you may end up a postal unit anyway and request F5 when you get to your unit.