Sometimes by trying to justify we can actually give fuel to the fire . You've resolved this and the important person in the conversation ( the one paying the money , the client ) has supported your mindset on it . Once you clearly state your standpoint on a suggestion in your area of expertise " no , I do not feel it would be of benefit , due to A , B and C " then its end of discussion . If the other person being retained wants to go on with it and push the point. Don't respond . Yes , send another group email after an acceptable time period , but change the direction of the conversation to what you feel is the next important step to complete the given task. Try not to have that period of self doubt . You got there shortly after where you felt vindicated that the client agreed with your viewpoint . You are in control . These are my skills , I stand by them . I will complete the task . If you drive into my lane I will calmly indicate around you and continue my course .