
Your recourse is going to vary by state and by university. Some have very strong protections for you, others not so much (like this is news). Your university should have a non-discrimination office. Contact them. Keep in mind that faculty have strong protections related to academic freedom. It allows them to speak in difficult subjects with some protection, but it also protects them in some inappropriate ways as well. This may fall into that category.
i would personally record audio as proof, though that depends on if your state is a one-party or two-party consent state when it comes to audio recording. you have the email to prove you alerted him, if you can/feel safe doing so i’d double down and say it directly to him in person so he can’t say he didn’t see the email if you report him for his behavior
While I agree, I’m also a Title IX investigator. I consider my university to have strong LGBTQIA+ protections. However, Title IX under the orange shitgibbon in the WH is very weak in this area. University policy may cover misgendering, but if OP was to reach out to DOJ or OCR, I have doubts that they would even open an investigation.