By request, here’s both my coming out letter and my Trans 101 FAQ, in case someone find them useful.
Feel free to copy from either, since mine were in part based on stuff copied from other excellent examples.
My HR director suggested I handle coming out as trans similar to how one would handle it is she needed to announce that she was pregnant and about to take maternity leave, i.e. this is something to celebrate.
So the email is intentionally relatively short, positive (i.e. no defenses about being trans or a litany of the struggles to reach the decision transition), and covered the essentials around what name/pronouns to use. I also explicitly asked for people’s support going forward.
The separate FAQ took a similar “light touch” tone, but got deeper into the likely questions people had. Although it too was intentionally brief. The FAQ was intentionally designed to start with Trans 101 in less than 10 bullet points, with an additional six bullet points about how to interact with trans people. Even if people stopped reading there, the basics were covered. The second part gave a bit deep explanation of each point, and the whole thing was kept to 5 pages, including a half-page of link to additional info in case someone wanted to learn more.
Of course it’s hard to beat The Axis of Awesome’s approach (NSFW language):