The Texas Senators give pretty clear instructions for the evaluation forms/letters of recommendation:
Senator Kay Bailey Hutchison -
Application Requirements-
6) Evaluation Forms: "...When completed,
it should be returned to you in a sealed envelope with the evaluator's signature across the seal." The applicant is then responsible for ensuring that the forms, along with signed acknowledgment form and transcripts, are received in her office by the deadline. My son sent these documents all together in one mailing envelope.
Senator John Cornyn
On the Personal Recommendation Form, instructions to the recommender, it states: "...
return this form to the applicant, along with any additional pages or letters, sealed in an envelope and signed across the flap." Again, son sent these letters to the Senator's office along with the other required documents (application form, resume, transcripts, etc...).
Our congressman, however, required that letters of recommendation, transcripts, physical fitness exam, etc... be sent to him directly by the person who filled them out. My son supplied a stamped addressed envelope for each of these.
As you see, each of the MOC have different requirements. You just have to read all the fine print!