about webmail installation

This forum isn't the appropriate place to post requests for technical assistance.

If you aren't sure how Drupal works--such as installing modules--you should start by going through some of the documentation. There's a Getting Started guide that can get you started on the road to using Drupal.

If you find you have specific questions you can ask those in (probably) the Post Installation forum. If you are asking about a specific module, your best bet for assistance is usually the support queue for that module.

one other thing-- its always best to start with the "read documentation" link for the module. You mention "webmail" which appears to be a dead module, so I'm assuming you mean "webmail_plus" which does have a "read documentation" link that leads to installation instructions.

You're not likely to find much success in forums unless you first demonstrate that you've read any existing documentation. for more info see http://drupal.org/forum-posting.