Revolutionary Irishman's correspondence (4)

I believe the answer is:

mail

'correspondence' is the definition.
(mail is written correspondence)

'revolutionary irishman's' is the wordplay.
'revolutionary' says the letters should be written backwards.
'irishman' becomes 'liam' (I've seen this before).
'liam' in reverse letter order is 'MAIL'.

(Other definitions for mail that I've seen before include "Armour of interlinked metal rings" , "Chain armour" , "protective cover" , "Letters - armour" , "American post from Lima" .)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app