Notes introducing the business of insuring landlords? (8,7)
I believe the answer is:
covering letters
'notes introducing' is the definition.
(a covering letter introduces somebody)
'insuring landlords?' is the wordplay.
'insuring' becomes 'covering' ('cover' can be a synonym of 'insure').
'landlords?' becomes 'letters' (people who let property).
'covering'+'letters'='COVERING LETTERS'
'the business of' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
(Another definition for covering letters that I've seen is " documentation to accompany goods maybe".)