You can go to the post office to buy two or more 22*18CM envelopes and use one as a return envelope, and the rest are just in case
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The reply time is not certain, it depends on the star's recent situation
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If you want to ask for a signed photo, because in It is almost difficult to buy photos of foreign celebrities in Taiwan, so when you send it, just write "I want your signed photo, I have attached a stamped return envelope" and basically the other party will give it to you.
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It is inappropriate to put money in it because Almost every celebrity has a lot to do, so you can't ask him to buy stamps for you!
You can go to a stamp agency to buy US stamps....it depends on which country you want to send to, go to the post office. Just check the postage...