Special occasion when the mail from communist arrives (3,6,3)
I believe the answer is:
red letter day
'special occasion' is the definition.
(I've seen this in another clue)
'when the mail from communist arrives' is the wordplay.
I cannot really see how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'from' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'arrives' could be 'a' and 'a' is found within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for red letter day that I've seen before include "Memorable event" , "Important occasion" , "memorable time" .)