Back in the "dark ages" when I asked for a letter of recommendation from my professors for medical school, I furnished them with a packet that contained the following:
- A copy of my CV
- A copy of my personal statement
- A list of the medical schools and locations (that I was applying to)
- A cover letter that contained the deadlines and addresses of where I needed the letter sent plus a thank-you.
- A waiver of my rights to see the letter.
- A stamped addressed envelope to my committee.
I personally delivered this packet to the professor (during office hours) when I asked them (face to face) if they would be willing to write a letter in support of my admission into medical school.
As soon as I had verification that the letter had been received by my committee, I sent a formal thank-you letter. I did not ever sent an e-mail other than to update them on my progress in the admissions process.
I didn't have any problems obtaining far more letters than I needed for this process.