I have some 100 users and I want to setdelivery options for these users at once.

Hi, Which version of Exchange and what options you want to set? If Exchange 2007 then you can create a powershell script to do it, like to change some option with set-mailbox for all the users in a OU. Get-Mailbox OrganizationalUnit OU Name | Set-Mailbox ..

Well I have Exchange 2003 with SP2 and I want to set Max number of Recipeints to be 20 for all 100 users.

You can modify it for bulk of userswith ADModify.Net... http://www.codeplex.com/admodify Option is available to change it in Exchange Features Tab after you select users... Introduction to ADModify.net