Ambitious type never opening highly impatient message? (2-6)

I believe the answer is:

go-getter

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'ambitious type' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for go-getter that I've seen before include "Informally, an agressive achiever" , "Someone whose career progresses rapidly" , "Person who is successful by being aggressive and energetic" , "Person who is successful through aggression and energy" , "Energetic and successful person - like retriever" .)

I've seen this clue in The Telegraph.

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