Would you go to a job interview in your sweatpants? Would you sent your CV with handwritten corrections? If you answer those questions with no, you might also want to write professional e-mails. The Free Software community is a tough environment when it comes to e-mail usage. This short guide tries to help you that the community perceive you as a professional communicator.
Quotation As a general rule: Do not quote the whole e-mail again, neither above your message, below or in the middle. Quote only the parts which are necessary. Use inline replying (for examples see Wikipedia's article on posting style) and trim messages if possible.
Subject Choose a good meaningful subject line. "e-mail", "help", "hello", or "questions" are not good subjects ;). When the topic of an e-mail changes, it helps to change the subject, too. Often it is beneficial to separated threads into different thread with different subjects.
Line break of e-mails Should be around 72 characters. Nobody will kill you if it is 70 or 74 or even 76. But a lot of people will get angry if you do not have a line break at all.
E-Mail signature Keep it small and simple. Signatures longer than
five lines should be avoided. The separated for the signature is "--"
(minus minus blank) and then line break. The blank is important as many
e-mail programs then know that it is a signature.
Mailinglists Use list-reply. It is not necessary to include the sender in To: or Cc: if he is subscribed. If the e-mail programs are configured correct the sender will be Cc'ed if he is not subscribed or wishes to be Cc'ed.
Forwarding e-mails When you forward e-mails try to give a short summary of the e-mail. Forwarding a huge e-mail thread to a list with only "FYI" will make you no friends.
General remark The better you structure an e-mail and the better you present the content -- the higher is the chance that people will read your e-mail.