When you use your address book to select recipients for an e-mail message or attendees of a meeting in Microsoft Outlook, information from your custom Contacts folder (
CRM Leads or
CRM Accounts) does not appear in the list.
In order to make it available mark your contact folder for use with your address book.
Select the contacts folder and open it's properties via the popup menu
Properties... or the ribbon
Folder > Properties > Folder Properties.
Folder Properties dialog navigate to
Outlook Address Book tab and set checkbox next to
Show this folder as an email Address Book.
Now when you create an email or meeting and open the address book
the folder is available in the dropdown