 If you liked
Mail
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 ...then you might like
Benkei in New York
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While the settings of both manga are different (one is set in Japan while the other is set in America), there are two commonalities between them - the fact that there's a detective that takes on extremely unusual cases, and that those cases are often solved at the end of the chapter itself.
So if you're looking for episodic mystery/supernatural cases that are solved, you can definitely pick up either of the manga.