Recently arrived special communication in informal bulletin (10)
I believe the answer is:
newsletter
'bulletin' is the definition.
(I've seen this before)
'recently arrived special communication in informal' is the wordplay.
I cannot quite understand how this works, but
'recently' could be 'new' (synonyms) and 'new' is found within the answer.
'special' could be 's' (common abbreviation as in Special Air Service) and 's' is found in the answer.
'communication' could be 'letter' (letter is a type of communication) and 'letter' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for newsletter that I've seen before include "Printed page" , "Sheet of information" , "Society report" , "Regular bulletin" , "circular?" .)