Inter-state or intra-state ?

Its inter state supply

When the delivery takes place at Mumbai, POS is Mumbai so CGST+SGST charged.

Intra-state.

As other person have Delhi GST number so Intra state

One of concept of GST that it is consumption base tax. So Place of Supply will be, where you deliver or hand over goods (not services). So if you are registered in Maharashtra and you deliver goods in Maharashtra to the person registered in New Delhi it POS will be Maharashtra and SGST + CGST should be charged. It is so because it is not sure that recipient will not consume the goods within the Maharashtra otherwise then New Delhi. So there must be a delivery agent for inter-state transaction.