What to with a rejection letter? Toss it? Frame it? File it? I say file it. I hear of struggling writers using them as wallpaper, but that would be a lot of letters.
There are two things a writer must do to receive a rejection letter. First, you must submit, and second, you must include a SASE. I always make sure I use one large enough and with enough postage for my manuscript to be returned. This way I can file the actual MS with the letter, and know which version I submitted.
I started a notebook with page protectors to file all correspondence from every submission. It is nice to go through it every once in a while just to remind myself that I am actually producing and submitting.
Yes, I reject rejection so I always tweak each returned MS and find another place to submit.
Until next time, keep writing.