Well, first, you should understand that mailboxes are just ONE reason to not create users directly in AD... remember SBS is an INTEGRATED, PRE-CONFIGURED product... the SBS Add User Wizard performs the following tasks (as noted on the first screen of the wizard):
Creates a user account
Creates a mailbox for the user
Creates a home folder for the user
Adds the user to security groups
Adds the user to distribution groups
Configures SharePoint access
Configures a disk quota for the user
Optionally sets up a client computer for the user
Additionally... the wizard will generate TWO welcome emails for the user which provide important information about the SBS environment.
When you add a user directly in AD, this is what THAT wizard will do:
Creates a user account
Creates a mailbox for the user
Because the AD method does not generate the welcome emails, the mailbox won't show up in the Mail Store until that user account logs on for the first time.
Hopefully that helps you to understand why you don't see the mailbox right away... and even moreso why you should never create a user that way anyhow.
Jeffrey B. Kane
TechSoEasy