They cannot use metered postage strips.
The stamps are exchanged for cash to stamp collectors and the proceeds are used to help pay for a few of the expenses incurred in their ministry to the Navajo Indians.
They realize it takes a long time for one individual to collect a good amount of stamps. Some suggestions for individuals desiring to help would be to ask some local businesses if they would permit you to put out a collection box with the explanation that cancelled stamps are being used to help Navajo Indian children get a good education.
Remember, even small amounts of stamps add up, so whatever you can send would be a great help. Get your friends and relatives to help collect and combine stamps for the best postage rate. There is UPS delivery to this address for large packages.
It is greatly appreciated if the stamps are trimmed from the envelope rather than torn, but this is not absolutely necessary. When trimming, please do not cut the "jaggies" around the stamp. THANKS! :-)