No more endlessly sending naughty messages - about time! (7)
I believe the answer is:
extinct
'no more' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for extinct that I've seen before include "Long gone, like te dinosaur" , "No longer living, like dinosaur" , "Having died out, animal species or volcano" , "killed off completely" , "Of volcano, no longer active" .)