Keep it short and to the point. 5 sentences or less (in the spirit of five.sentenc.es).
State clearly what you want and make it easy to answer.
Make your subject as specific as possible.
Add the code [NRN] to the subject if no reply is needed.
Specify the urgency in your subject using these codes: [MONTH], [WEEK], [DAY], or [ASAP].
Optional: Add a link to your website or blog.
Optional: Write a short bio about yourself in 160 characters or less.
More generally, please follow the Email Charter.
Subject: Project proposal accepted [MONTH/NRN]
This is just to inform you that our proposal has been accepted. Hooray!
Bio: I'm a senior developer at...