Take jacket off briefly while at post, though it's meant to be protective (4,2,4)

'take jacket' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?

'briefly while at post though it's meant to be protective' is the wordplay.
I cannot really understand how this works, but
'at' is within the answer.
'post' could be 'mail' (synonyms) and 'mail' is found within the answer.
The remaining letters 'coof' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'off' acts as a link.

Can you help me to learn more?