Sending E-mail To Requesters

Ok, I'm in the process of configuring our ServiceDesk Plus application and my boss originally was the one that set it up and configured the mail settings, importing the requesters using Active Directory, etc.

So, my question is...how do I send an e-mail to all requesters on the system once we're ready for them to use it for the first time?

The Admin Guide tells you how to do this if you're creating a new requester, but I want to know how to do this if they are all already created and maybe the initial setup didn't send an e-mail out because the mail settings might of been configured after the users were imported from Active Directory?

Any help is greatly appreciated...thanks!