These are guidelines (some lists make them into hard-and-fast rules). Say you belong to a mailing list. I belong to the devon-l @ rootsweb.com list. They even have an item within their FAQ which gives you some guidance on how to frame the sort of query which will get looked at. It all starts with the subject line. Whatever you do, don't have a subject line which only says something like 'help' or 'my brickwall ancestor'. The reason is that there are several very Kind Souls who are only to happy to help if they can, but they belong to several mailing lists and need to be able to pick out the ones where they might be able to help, while deleting the ones with the ghastly subject lines above. After all, the one which says merely 'help' could be asking 'what type of lawn mower should I buy?', couldn't it. So you would put in the ancestor's name (surname in CAPITALS), dates, place: like
John DOE, b 1785 Alphington, Devon
And in the body of the message, Devon-L recommends " Incidentally, it is always a good idea to include with any query to the DEVON mailing list a brief indication of what searches of online and conventional sources you have already made. This is in order to avoid your receiving, and other respondents wasting effort providing, information that you are already familiar with."