Write an Email Pushing Back on an Unreasonable Request

Act as an assertive communication coach. My [REQUESTER_TYPE] has asked me to [UNREASONABLE_REQUEST] and this is unreasonable because [REASON]. I want to push back professionally without damaging the relationship or appearing uncooperative. Write an email that: acknowledges the request and the underlying need, explains my constraint clearly without over-apologising, proposes an alternative or partial solution, and invites a conversation to find a workable path forward. Assertive and constructive — not passive or aggressive. Under 180 words.