Deposit of 10c enclosed in dispatched mail (8)
I believe the answer is:
sediment
'deposit' is the definition.
('sediment' can be a synonym of 'deposit')
'in dispatched mail' is the wordplay.
'in' indicates putting letters inside.
'dispatched' becomes 'sent' (I've seen this before).
'mail' becomes 'dime' (I can't justify this - if you can you should believe this answer much more).
'sent' going around 'dime' is 'SEDIMENT'.
'of 10c enclosed' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sediment that I've seen before include "Matter sinking to the bottom of a liquid" , "Material settling out in a liquid" , "Matter settling out in liquid" , "Silt" , "Residue" .)