Use this as a structure, not as a copy-paste template. Professors can recognise generic emails. Replace every bracket with your real details and adjust the tone for your field.
Subject: Prospective PhD applicant - RTP 2027 - [your research area]
Dear Dr/Professor [Name], I am preparing an application for a [PhD/MPhil] at the University of Sydney for [research period/year], and I am writing to ask whether my proposed research may fit your supervision interests.
My proposed project examines [one-sentence research problem]. I am particularly interested in [method, population, dataset or theory]. Your work on [specific publication/project/theme] is closely related because [one-sentence connection].
I completed [degree] at [university], where my research focused on [brief thesis/project]. I have attached my CV, transcript and a short proposal for your review. If the topic is within your current supervision capacity, I would be grateful for the opportunity to discuss whether it may be suitable for a University of Sydney research-degree application.
Thank you for your time and consideration. Kind regards, [Your name].