In what way does the postmaster feel out of place in the remote village?
The postmaster feels out of place due to the fact that he must interface on a daily basis with strangers. Essentially, the postmaster finds it difficult to relate to the villagers, who possibly represent the kinds of people he has never had to associate with before.
The men employed in the indigo factory had no leisure; moreover, they were hardly desirable companions for decent folk. Nor is a Calcutta boy an adept in the art of associating with others. Among strangers he appears either proud or ill at ease. At any rate, the postmaster had but little company; nor had he much to do.
Perhaps the factory employers come from dissimilar castes; the narrator doesn't say, but the implication is clear. The postmaster considers the workers "hardly desirable companions for decent folk" like himself. In the story, he has "little company" because he finds it difficult to integrate into the fabric of daily life among the villagers. Also, since he has little to occupy him, the postmaster feels ill at ease.
Aside from these difficulties, the postmaster also misses his family. This is another reason he feels out of place: his family isn't with him. They are back in Calcutta.
On some evenings, seated at his desk in the corner of the big empty shed, the postmaster too would call up memories of his own home, of his mother and his sister, of those for whom in his exile his heart was sad,—memories which were always haunting him, but which he could not talk about with the men of the factory...