Asia - From Yangon to Kawathaung overland?

Is there a way to make this trip via rail of coach? I am wary of the domestic air service in Myanmar. Thanks!

No rail service down to the far south. I believe that no road travel is permitted below Thanbyuzayat (south of Mawlamyine) without special permit, and I've not heard of any being granted to foreigners. This has been long-standing situation so if something recently has changed, maybe somebody here can chime in. By road I have only been to Thanbyuzayat and no further and due to checkpoints, pushing on wasn't possible.

I don't think there is boat or air service (at least not regular public service) between Mawlamyine and points south.

Options:

1) By ship from the Yangon/Irrawaddy delta area, but sailings are very infrequent so impractical for most travelers.

2) By air Yangon-Dawei then by boat to Myeik then Kawthaung.
3) By air Yangon-Myeik then by boat to Kawthaung.
4) By air Yangon-Kawthaung

Domestic Logistics to these places need to be figured carefully, as flights/boats are not necessarily daily and coordination is sometimes hard to do. You need schedule flexibility. These flights are highly subject to last minute cancellation. As for flying, from Yangon you can look at Air Mandalay and Yangon Airways to see what they've got, probably a better choice than Myanma Airways which also flies to each of these on older planes. There's also Air Bagan, which is on my personal boycott list because of its gangster ownership in cahoots with the generals.

My personal choice of the options to balance logistics and expediency with sightseeing interest, would be #3 via Myeik and the Mergui Archipelago.