I would like to send some bulky (but light weight) items from Bangkok to Phuket and from Bangkok to Chiang Mai.

What are the various ways for me to send, besides EMS and Registered Parcel. I'm afraid my box is too big for the post office to accept. Are there some companies out there offering delivery services via land, train etc?

Yes, there are other services. Most tour bus companies and the SRT (train) offer this service. Mostly reliable but not advisable for fragile or perishable goods. Also those services are only station to station (consignee has to collect it at the arrival station) whereas EMS is delivered to the home/office of the consignee. Check with your local post office about size limitations. EMS is very cheap here inside Thailand and very reliable and fast.

opalhort

Try Thailand Post. I was at the post office yesterday and there was about 6 boxes about 185cm high (about 6ft) and 120 cm (about 3-4ft) being posted. They can also post motorbikes.

Nothing ventured nothing gained.

Thai Post will pick up and and send a refrigerator so I think this bulky item will go also. I hear they will send a motorbike also. We sent my wife's family a medium size fridge via Thai Post last year no problem.