Half of them were not well and sent message (7)
I believe the answer is:
emailed
'not well and sent message' is the definition.
I can't judge whether this definition defines the answer.
'half of them were' is the wordplay.
'half of' means to take half the letters.
'were' becomes 'ailed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'them' cut in half is 'em'.
'em'+'ailed'='EMAILED'
Can you help me to learn more?
(Other definitions for emailed that I've seen before include "Contacted" , "Communicated with" .)