Is "keep up the good work" a polite thing to say to your co-workers? I'm under impression that only someone from higher position has the privilege to say this.
When replying the emails to a co-worker, who is not a subordinate of yours, is "keep up the good work" a proper phrase in this case?
What other praises I could use to express my sincere respect on what they have achieved, instead of a perfunctory "good job!"?