Railway Reservation is avilabele in following post offices in mumbai
1.GPO
2.Girgaon
3.Mandvi
4.Dadar
5.Sion...
more...
6.Powai IIT
7.Chembur
8.Ulhasnagar
9.Antop Hills
10.Nerul Node
11.Chinch Bunder
12.Bhivandi
13.Dandekar Wadi
14.Kurla North
this is according to display board at reservation counter at CSTM