IQ Test Quotes #23

It’s a 7 letter word.
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If we remove 1 letter from it, it remains same.
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If we remove 2 letters from it, it remains same.
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If we remove 3 letters from it, it remains same.
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If we remove all the letters from it, still it remains same.
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What is it ?
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.Answer: POSTBOX/MAILBOX