Writing rejection letters is a tricky undertaking.
On the one hand, you want to be clear and straightforward, getting your meaning across without misunderstanding.
On the other, you want to do it with enough tact to avoid being mean and inconsiderate of the recipient's feelings.
There are two primary formats for rejection letters: indirect and direct.
One is designed to keep the door open for establishing a relationship within the short-term, while the other just shuts it (at least, for the meantime).
You can use either of the two, although you must realize that they are likely to elicit different responses from your readers.
The indirect format begins by thanking the recipient and building up the possible reasons for rejection in the reader's mind.
Once you develop the rationale for the negative decision, that's when you actually give them the actual rejection, essentially dampening the blow.
Use this when you want to ensure that the relationship, despite this particular rejection, stays in good terms.
The direct format pulls no punches and starts out with the actual rejection.
You can choose to give a reason or not, although, it's always good practice to let people know why they're being given the shove.
It's just the courteous thing to do.
Do note that if you're giving a reason for the verdict, keep it short.
Doing too much can dilute the rejection message.
In both cases, make sure to use a professional writing software.
The last thing you want to do when giving a notice of rejection is to mistakenly relay something else you didn't mean.