How to avoid lighting seams with connecting geometry?

I'm working on creating a tileable set of hallways with Maya, and on import to Unity I find that the seams are very apparent when snapping pieces together. How can I force the lighting to work with two different pieces of geometry?

An example of what I'm talking about; the line is where the two pieces meet:


Use a mesh-combiner utility to merge the tiles into a single mesh at runtime. When your merges start getting too big (vertices > 65000), use props to hide the problem (crates, doorframes, etc.), and start a new section of merging.

I think the default mesh-combiner in Unity is called CombineChildren and is in Standard Assets, but there is at least one more available in the forums.