The most common and most likely answer to this crossword clue is the 6 letter word FRANKS
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More clues leading to the result FRANKS
Buddy explains!

The straight part
We know that "stamps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stamps = franks.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FRANKS mean?
FRANKS noun- Free postage, a right exercised by governments (usually with definite article).
- The notice on an envelope where a stamp would normally be found.
- To place a frank on an envelope.
- To exempt from charge for postage, as a letter, package, or packet, etc.
- To send by public conveyance free of expense.
- A hot dog or sausage.
- The grey heron.
- A pigsty.
- To shut up in a frank or sty; to pen up; hence, to cram; to fatten.