Below are some rules which should govern all messages sent to any MailList. If you are not familiar with standard MailListEtiquette please take a moment to read through these rules as they greatly facilitate email communications.
Plain Text - All messages sent to the list should be in plain ASCII text. HTML, rich text or stylized messages should not be sent.
No Attachments - Attachments should not be sent to the mailing list. This includes HTML email, Vcards and other ugliness (PGP signatures are okay). If you want to share a resource please post a URL to the content rather then attaching it to your message.
Quote Appropriately - When responding to someones message remove all the parts of their message which aren't necessary for context. In particular don't leave the entire message quoted below your response. The mailing list archives are available to people who need to remember what was said in past messages.
Be Courteous - It's easy for fights and flame wars to erupt on mailing lists, you don't need to contribute to them.
If you must flame someone do it off list, if you think the list needs to know why they are wrong, please point out errors in their argument or logic rather then flaws in their personality or beliefs. Give Credit - If you repost information from another source make sure you give credit to the original source, ideally as a URL.
Add Value - Your email message is going to nearly 500 peoples' mailboxes, if it doesn't add value to the discussion please don't post it. This includes jokes, bitchy comments as well as "me too!", "yeah" and "right on!" posts. If you feel it's important to show support for an idea in this way please do so off list.
Don't Spam - Please keep self promotion, especially commercial self promotion, to a minimum. If your product is directly relevant to a discussion at hand please let us know, otherwise wait until someone asks.
Appropriate Signatures - Signatures should be under five lines in length. Signatures declaring that a message is confidential, copyrighted or otherwise restricted need to be removed before posting to a public forum and will not be honored if they remain.
Reread Before Posting - Respect other list members time and effort. Before you hit send take a moment to reread your post, make sure the message is going where it is supposed to, that you are saying what you meant to and that the spelling and grammer is decent. All of these things will help your opinions and thoughts be taken more seriously.
Educate Newbies - If someone is having problems following these rules please send them a polite message off list pointing out what they are doing wrong and how they can fix the problem.
Source: MailingListEtiquette