It’s just like sorting mail, sir (7)
I believe the answer is:
similar
'it's just' is the definition.
I can't tell whether this definition defines the answer.
'sorting mail sir' is the wordplay.
'mail sir' anagrams to 'SIMILAR'.
Though, I am not sure how this is indicated.
'like' is the link.
Can you help me to learn more?
(Other definitions for similar that I've seen before include "Comparable" , "Resembling, like" , "Alike, resembling" , "Of the same kind" , "Akin" .)