The background

Three years ago, I sent a manuscript to a major publisher who took direct submissions (as opposed to only agent-pitched works). I was optimistic about the manuscript, as I am always optimistic while sending manuscripts off.
I shouldn’t have been, I guess. Three years later, I received an email from the editor, form letter, that said they rejected the manuscript.
Three years later! I forgot I had written them. I don’t remember what manuscript I sent them!
Gratitude
I am grateful for the rejection. It wasn’t the nicest or most personal rejection I’ve gotten, but it is by far one of the best. Three years ago I wasn’t as good a writer as I am now. I have learned much in those three years and improved my manuscripts with the help of developmental editors and re-edits. Looking back, I wouldn’t have been proud of that document if it had been accepted.
So I will try again with another book (if I can figure out which book) and a new cover letter and send them another, if I can bear the three-year wait time. Ok, maybe not.
Catch me in the comments
What’s the best rejection you’ve ever had?