I’m an USA passport holder and departing Bangalore airport via Bombay. Where do I complete immigration formalities?
I assume that you are travelling from Bengaluru to the US via Mumbai but that's hard to tell from your question.
The most likely order of events is:
- For check-in (online or in Bengaluru) you need to present your US passport
- Bengaluru to Mumbai is a domestic flight. No immigration involved but you still need a document for ID verification.
- You will go through Indian exit immigration in Mumbai
- You will go through US entry immigration in your first port of entry in the US
- Any subsequent travel within the US does not involve immigration at all.