Usually it is for one of the following reasons:
It is of the ``It doesn't work. HEEELLLP!!!'' variety. Such messages are often ignored by people on the mail list. (They figure you need help if you are posting a question.)
The question is posted in HTML. Many people don't have HTML-capable mailers and will not bother to read it. Your message is more likely to be answered if you put it in plain old ASCII format.
You used the wrong return email address, or you spam-blocked the email address. Most people will not field the instructions nor bother to re-send when it bounces.
The subject line is not informative. ``[item-list] tag'' is better than ``It doesn't work''.
Information needed for support is not included or is not intelligible. Version of MiniVend, operating system and/or virtual server type, HTTP server (i.e. Apache), and database types in use are all relevant to most questions.
Question is answered in this FAQ, the README, or by doing a simple text search (with keywords you mention) in the documentation. Most people won't do manual reading for you -- they expect you to take the time yourself.
The message does not mention what is in all of the error logs, i.e. both the main error.log and your catalog error.log. HTTP server error log entries are also nice to know about, though it is understood that many people don't have access to them.
The message does not mention what is NOT in the error logs. If you don't mention it, it will be presumed you did not look.
No one knows the answer.