Ouch! Of course, you're absolutely right... although the two are so often so closely associated (Customs and Immigration - one following the other) that there is usually no need for specific distinction between the them. That said, clearly in this particular case, there IS a very important distinction to be made and I admit I should have said "I thought it was still possible to clear immigration in some other Thai airports"... Hopefully NoY knew what I meant anyway but I apologise for any confusion caused as this was certainly not my intention...

I fly very regularly to BKK but don’t normally fly immediately to another domestic airport (think the last time I did this was to CNX in November last year - when I definitely cleared immigration in Chiang Mai) so my information could well be out of date but if it is, then it seems I’m in good(?) company as so is Thai Airway’s own website which clearly states:

International to Domestic

If your final destination is Chiang Mai, Chiang Rai, Hat Yai, Krabi, or Phuket, you then proceed to Transfer Check-in desk on the second floor of concourse A/B. The Immigration and Customs formalities will be done at your destination airport. Transferring to other domestic airports or having baggage checked only to Bangkok , you must land, pick up your baggage, proceed through Passport and Customs Control formalities and check in at Row C on the fourth floor of PTC.

Taken from: http://www.thaiair.com/Travel_Destin...lighttrans.htm

I’m really NOT trying to confuse things, in fact, I’d really like to know… as I am sure NoY would too… but has the above information now ceased to be correct?