Jo Hund's Email Style Guide
This style guide applies to Writing Emails. It is part of Jo Hund's Software Engineering Guide.
Always have a subject. Make sure the recipient gets the essence of your message even if the subject is all the recipient ever reads. If you share more than one project/context with the recipient, prefix the subject with the project/context name:
'TIRO | Server update: new permissions'
Follow guidelines for technical writing in the Technical Writing in English Styleguide
Some people use their inboxes as todo lists. If possible limit the scope of each email to a single topic so it's immediately obvious what the todo related to your email is.
I often start writing an email and develop my thoughts as I write. It's good to let the email sit for a few minutes. Do something entirely different and come back with no implicit context. You will notice all kinds of interesting omissions and unnecessary text. Clean it up and insert the executive summary at the top of your email.