Originally Posted by JBKettle

You can't walk to E from any terminal post-security. They could, however, clear security in D, walk to High-C, and take the Skylink from High-C to Low-E and walk the final portion to their gate.

There is -finally- a C-to-E connection in the plans, which would indeed connect all terminals by foot post-security. IIRC, it is slated for later this decade, unfortunately.