The Lake House.

When architect Alex Wyler moves into an unusual glass house on stilts over a lake, he discovers a note from the previous tenant in the mailbox--but no one's lived in the house for years. He replies and soon discovers that he's corresponding with a doctor named Kate Forster. Their correspondence, only through the 'magical' mailbox, turns romantic and their paths cross in unexpected ways, but when they try to truly connect, danger looms. They must try to unravel the mystery behind their extraordinary romance before it's too late.