How many letters of recommendation do I need? Although it can vary, generally, you will be asked for three letters. We recommend that you send only the number of letters requested. Admissions committees do not have enough time to read extra credential.
It’s always a smart idea to offer to write a letter of recommendation for a colleague who you know is well qualified for the job in question. Consider it good career karma; after all, you never know when you’ll need a letter of recommendation for yourself, and your colleague may be happy to return the favor.