When you install Mailman from a third party package, your primary support resource should be the packager. The packager knows what's in the package and how it should be configured. People on the firstname.lastname@example.org don't always know these things.
For a more detailed and eloquent presentation of this idea, see http://mail.python.org/pipermail/mailman-users/2011-June/071769.html.
The same considerations apply if you followed a third party HowTo document. Plus, there may actually be errors or unaccounted for situations in the HowTo and the author should be made aware of these things. Thus, you should at least try to contact the author of the document first.