Adoptees face a special problem with genealogy--so do their children and grandchildren

About 6 months ago I got an e-mail from a stranger whose father I barely knew, but we'd attended the same high school. His father was deceased and had been adopted as a young child, so the question was, could I help him find his father's birth family. We chatted a little (via e-mail) and I told him what I could (mostly small town gossip where everyone knew everyone else's business). I heard from him today, he'd done two DNA services and got the same results--a second cousin from a town near where his father and I had grown up--so probably a connection to the elusive grandfather. He's over the moon. He's done extremely well in life, has a wonderful family, good education and great career. But he just always wanted to know. . .