When you add a new user and their email address doesn't show up in the Global Address List, work through the tips and suggestions in the ever-useful Exchangepedia Blog: http://exchangepedia.com/blog/2005/11/new-user-does-not-show-up-in-gal.html
Bulk-add new users with the script here (http://www.exchangepedia.com/blog/2006/11/exchange-server-2007-bulk-creation-of.html) or give existing users mail access (http://exchangepedia.com/blog/2006/12/bulk-mailbox-enabling-users-exchange-shell.html - this also has details for adding multiple meeting rooms as resources). And when an employee gets replaced, the steps at http://exchangepedia.com/blog/2006/03/how-to-reconnect-mailbox-to-another.html make it easy to connect the previous user's mailbox to the new user account so that mail for that job role keeps going to the right place.Reject spam with a custom message Just in case the message you're rejecting comes from a real person, you can have Exchange send a less cryptic message that the default error; it will make your customers look more professional. This blog post http://mostlyexchange.blogspot.com/2006/12/exchange-2003-sp2-imf-tuning.html
explains how - but make sure to keep the 550 error code at the beginning.
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