Very much to Gayle's point:
"What is a "group mail"?
As a platinum member, you can send 'group mails' to up to 100 colleagues.
To do so, use the 'search for pros' option to select a group that meets certain parameters (for example, language pair, credentials, areas of expertise, etc.) Then click "compose" in the yellow box marked 'Group Mail'. Your message will be sent to up to 100 people who met your criteria.
You can imagine many uses for this: finding someone to help you on a project, starting a team, etc. The function is not to be used for sales, though. "
It is something that should be used when there is a reasonable chance that the recipient and sender might both find it useful, and as it says, is expressly not for sales.
[Edited at 2003-09-27 11:40]