Sorted out the mails I had lost (7)
I believe the answer is:
mislaid
'lost' is the definition.
(similar in meaning)
'sorted out the mails i had' is the wordplay.
'sorted out' is an anagram indicator.
'i had' becomes 'I'd' (contraction).
'mails' with letters rearranged gives 'misla'.
'misla'+'id'='MISLAID'
(Other definitions for mislaid that I've seen before include "Temporarily lost" , "not to be found?" .)