If you want to stop the mailings this what you do:
Each request comes with a response card and a return envelope.
Cross out your name on the response card and write: Please take my name off your list.
Place in the return envelope. DO NOT WRITE YOUR NAME AND ADDRESS ON THE ENVELOPE.
If the envelope DOES NOT have postage, the organization/agency will be charged the postage which is usually double the going rate for a stamp. You become a liability not a potential donor.
If the envelope HAS postage send anyway. They will read your note and remove you from their database.
Nice. No. Effective. Yes.