A client recently asked me to change their address policy so they all showed as lowercase.

First you’ll need to create new email address policy from the Exchange Management Console – organisation Configuration – Hub transport, click on the E-mail address Policies tab on the right.
Right click on the space below and go to New E-mail address Policy.

Follow the Wizard, it doesn’t matter too much what you put in here as the command we’re about to run over rights the settings. Once that’s complete open the Exchange Management Shell and run:

Set-EmailAddressPolicy -Identity “Policy Name” -EnabledPrimarySMTPAddressTemplate “SMTP:%rAa%rBb%rCc%rDd%rEe%rFf%rGg%rHh%rIi%rJj%rKk%rLl%rMm%rNn%rOo%rPp%rQq%rRr%rSs%rTt%rUu%rVv%rWw%rXx%rYy%rZz%1g%s@yourdomain.com”

You should be good to go, hope this helps.