It may mean the sack to postal workers (7)
I believe the answer is:
mailbag
'it may' is the definition.
The definition suggests a singular noun which matches the answer.
'the sack to postal workers' is the wordplay.
'the sack' becomes 'bag' (I've seen this before).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'postal workers' becomes 'mail' (I can't explain this - if you can you should give a lot more credence to this answer).
'bag' after 'mail' is 'MAILBAG'.
'mean' is the link.
Can you help me to learn more?
(Other definitions for mailbag that I've seen before include "Sent down sewer's product" , "carrier" , "Postal sack" , "Container for carrying letters" , "One sewn by convicts" .)