You could simply send IRCs, so that the receiver can change them into stamps, pay for postage and send your letters back to you. IRCs are not common anymore, but you can still get them at some post offices. You should shop-around a bit though.

Or you can also include stamps (of the country where the receiver is in) and an SAE, which is known as an SASE. For example, if you're writing to someone in the US, then you should include US stamps with SAE, since USPS doesn't accept foreign stamps.

Hope this helps you!

Can anybody tell me how i can get my letters back from out of the country without sending cash. I asked the people at my local post office and i got no help. Thanks