I've had a few grim rejections in my time. One gem was a rambling 400-word monologue from a publisher who managed a dozen crass spelling mistakes in telling me I wasn't joining their club (which brought Groucho Marx straight to my mind).
However, I did receive an exceptionally positive rejection last January: the editor had taken the time to go through my poems one by one, explaining what they liked and didn't like, giving their reasons on each occasion and suggesting alternative routes. They demanded that I reassess my poetics. The initial pain of rejection meant that I knew I had to put the manuscript in a drawer for a few months and then go back to it without prejudice, so that's what I did.
I've spent the last two months chiselling away at those poems, using the editor's remarks as a point of departure, sometimes agreeing, sometimes disagreeing, but always reacting to the challenge that was so generously set. I'm determined not to lose my identity as a writer in the desire to be published, but this is a great chance to develop further.
I would have loved an acceptance last January, but I'm convinced I'm now a better poet for having received such a constructive rejection. This improvement, deep down, is my goal.