Rubbish I send, filling empty Microsoft Outlook (7)
I believe the answer is:
mindset
'outlook' is the definition.
(I've seen this before)
'rubbish i send filling empty microsoft' is the wordplay.
'rubbish' indicates anagramming the letters (a poor quality or rubbish spelling of the letters).
'filling' means one lot of letters goes inside another.
'empty' says to hollow out the word (remove centre letters).
'microsoft' with its centre taken out is 'mt'.
'i'+'send'='isend'
'isend' anagrammed gives 'indse'.
'indse' placed inside 'mt' is 'MINDSET'.
(Other definitions for mindset that I've seen before include "convictions" , "thinking normally" , "way of thinking" , "fixed attitude" , "Outlook" .)