Make sure you use the list only for the stated purpose . For example, if your list is about one product, don't start sending promos on others. One thing you could do however, is have a paragraph in your regular announcement to promote your other product. If appropriate, have a copy on your web site with the hyperlink clearly indicated at the top of the e-mail, this allows you to have a more appealing HTML version for those that want it. If your list is ad-supported, don't open with an ad this will avoid having your readers think they are victims of a spam.
Discussion list Have a good list FAQ .
The FAQ should of course have information about the dos and don'ts of the list but also define what the topics are. Have the URL to the FAQ included in the header of each mail. If you can configure your server to strip attachments , do so. Besides they could be sending embedded viruses without even knowing it, reflecting badly on the list operator. Try to make sure that auto remailers don't go through to your list .