Originally Posted by ohsopc

All international passengers who are connecting to any domestic destinations will have to clear immigration at Suvarnabhumi Airport. They then will enter A/B Pier which are for domestic flights. Customs will be done at their final destination (HKT, CNX, etc.). Where they will have to walk past the normal baggage claim and enter the International baggage claim to clear customs. So no, no one can illegally enter the country.