Stop Spam Email

My aunt has just gone into a nursing facility, and the family is wondering what is the best and fastest way to stop all the excess mail from these groups - she is on a limited budget and cannot afford to send contributions, plus she gets so many requests it will flood the nursing home mail.
Contacting each one would be very expensive, as she is receiving from 50+ groups, and most of them do not enclose postage-paid envelopes. I am looking for something like the “Do Not Call” site for unwanted phone calls.