A simple question: in summer 26 I plan to fly to bkk but not stay, only to fly onwards to Malaysia for a month, then back to Thailand and to ENTER for a month. So basically buy a return ticket London-bkk but transit on arrival. Do I have to go through Thai immigration on arrival, or stay in airport to catch flight to KL?
TLDR : Answer Summary
If you're flying into Bangkok and then transiting to Malaysia without picking up any luggage, whether you clear immigration or not depends on how you booked your flights. If you have two separate tickets, you will need to pass through immigration to check in for your Malaysia flight. However, if you booked a multi-city ticket on one reservation, you can stay in the transit area without going through immigration.