Select the recipient types you want to include. You can select All recipient types or The following specific types. If you select The following specific types, you can select one or more of the following recipient types:
Users with Exchange mailboxes Select this check box if you want to include users that have mailboxes. Users that have Exchange mailboxes are those that have a user domain account and a mailbox in the Exchange organization.
Users with external e-mail addresses Select this check box if you want to include users that have external e-mail addresses. Users that have external e-mail accounts have user domain accounts in Active Directory, but use e-mail accounts that are external to the organization. This enables them to be included in the global address list (GAL) and added to distribution lists.
Resource mailboxes Select this check box if you want to include Exchange resource mailboxes. Resource mailboxes allow you to administer company resources through a mailbox, such as a conference room or company vehicle.
Contacts with external e-mail addresses Select this check box if you want to include contacts that have external e-mail addresses. Contacts that have external e-mail accounts do not have user domain accounts in Active Directory, but the external e-mail address is available in the GAL.
Mail-enabled groups Select this check box if you want to include security groups or distribution groups that have been mail-enabled. Mail-enabled groups are similar to distribution groups. E-mail messages that are sent to a mail-enabled group account will be delivered to several recipients.