1.  Mail offices are of two kinds.  They are  -Sorting Mail offices  -Transit Mail offices  A sorting mail office situated in a railway station is called a RMS office.  A sorting mail office situated outside the Railway station is called a Sorting office.

2.  A branch of RMS which deals with the closed bags is called transit mail office.  A transit mail office functioning in a train is called a transit section.  Head Sorting Assistant is the in charge of the Sorting Mail office.  Mail Guard/Mail Agent is the in charge of the transit mail office

3.  Sorting Mail office handle bags and contents of bags.  Receive,close, despatch all kinds of bags  Open all kinds of bag addressed to them and sort all kinds of articles received by them.  eg. Madurai RMS, Karaikudi sorting office  Head sorting Assistant is the in charge of the office

4.  Handle closed bags  Receive, close and despatch all kinds of bags  Open transit bags addressed to them and sort only closed bags  Never sort the articles  Mail Agent/Mail Guard is the in charge of the Transit Mail office

5.  Automatic Mail Processing Centre  situated in cities where the quantum of mail is heavy.  Mechanized coding and sorting of unregistered mail.  At chennai, Mumbai and Delhi  Press sorting office  situated on the premises of the News Paper.  This office works to suit the dispatch timing of the News Paper.

6.  Packet Sorting office  situated in big cities where volume of second class unregistered mail is very high.  CRC  the registration branch of the Mail office, where the processing of registration work is done on computers.  A CRC can be situated in the Mail Office itself or in a separate location

7.  Corporate mail office/ Bulk Mail Centre  opened in big cities.  Mails are received from bulk Mailer  i.e is firm which is capable of posting of 5000 unregistered articles/250 registered articles in sorted destination wise bundle.  The Bulk Mail Centre despatch the bundle.

8.  Business Post Centre  Performs premailing activities for a fee.  collection, insertion, pasting, addressing, franking/affixing stamps.  Record office  stationery office of the Railway Mail Service where the work papers of the sections attached to it are prepared.  Head Record office  a stationery office  situated at the headquarters of RMS Division  prepares salary and contingent bills for the entire division

9.  Sub Record office  stationery office of the RMS,  situated at the same station as a Mail office.  Prepare work papers for sections and themselves.  all forms required for their sections are supplied.