Hi @Stompythedinosaur
I can't speak for the poster you replied to but for myself:
When people add pronouns to "support trans people" they are supporting the belief that the difference between men and women is mental rather than physical, and therefore they are supporting the reallocation of resources set up to help the female-bodied thrive in a sexist society from those female-bodied people to those with a "female mind", whatever that is, and the undefining of female-bodied people as a social group with their own rights, concerns, priorities deserving of a political voice.
As a female-bodied person, it harms me to lose those resources and that political voice, an it harms me to be redefined as a person with a female mind when that is not something I identify as, simply because the words I have always used, and society has always used, for the female bodied have been redefined without my consent.
I am very happy to listen to trans people with respect to their experiences, so I know trans people do not speak with one voice. I find it sad and strange that the people who wish to appropriate female words and spaces do not feel any need to respect my needs and experience, and that of the many, many women like me.
I hope you realise that I am not telling you whether to put pronouns in your email or not. That is up to you. I am simply making sure you are clear that it is harmful to people like me who understand ourselves to be female but do not have this "female brain". What you do with that knowledge is up to you.
HTH.