Short question,

I have a scheduled flight tomorrow Chiang Mai - Bangkok - Tokyo with TG. How is the check-in and immigration handled? Do I go through domestic in CNX first and then through the immigration in BKK or can I use international departure in CNX and everything is checked through?

if you checkin at international desk at CNX, you will clear immigration here. they give you a sticker called CIQ and you transfer to intl terminal at BKK without exiting the secure area.

Yup; You can do it both ways, but outbound it's definitely better/faster to go through immigration in Chiang Mai. And your bags will get checked all the way through.

Coming back it's also faster to do it in Chiang Mai, just that customs is more likely to check your bags; not a problem if you don't carry anythign out of the ordinary.

Exactly what I wanted to know! Thanks a lot!