If you're responding to a previous post, quote accordingly, but judiciously. This helps put your comments in context, yet avoids messages that are too long. Some mailing systems mangle the information in the header with your address. If you have a response, consider responding directly via email if you think no one on the list will be interested. Watch your temper.
Email sometimes makes tempers flare.
If you think you should wait or tone down your note, you most likely should. Don't type in all capital letters. Finally, employ common courtesy. If someone helps you out, a thank you will be appreciated. While not part of netiquette, the value of mailing lists should be approached like other many other sources of information, such as a newspaper or a journal.