I shall go to Muscat from Kolkata via Mumbai through Jet Airways in the same PNR. Where should I clear immigration? At Kolkata or at Mumbai? Thanks.
#1 doesn't make any sense. Immigration is entering a country.
"#1 doesn't make any sense. Immigration is entering a country."
For countries that have outbound border checks it's the immigration officers that perform the check, so strictly speaking it *is* an immigration check. I try to use the terms "outbound immigration" or "exit formalities" to distinguish between exit and entry.
OP, you will have your Indian outbound immigration check at Mumbai (BOM). You will also need to reclear security at BOM, even if making an airside connection. Indian security does not recognize their own checks at previous airports.