A little ship going round, one holding mail items? (11)
I believe the answer is:
philatelist
'one holding mail items?' is the definition.
(stamp collector)
'a little ship going round' is the subsidiary indication.
'going round' indicates an anagram.
'a'+'little'+'ship'='alittleship'
'alittleship' anagrammed gives 'philatelist'.
(Other definitions for philatelist that I've seen before include "Person with hobby" , "Stamp collector" .)