How many names can I include in a distribution list?
The maximum number of names that you can include in a distribution list depends on the size of the contact files (for each contact). In general, for users of Microsoft Office Outlook 2007 Service Pack 1 or earlier, a distribution list can contain between 50-70 names and e-mail addresses.
2007 Microsoft Office Suite Service Pack 2 (SP2) removes any limitation to distribution list size. If your computer has Office 2007 SP2 installed, you will be able to create and use distribution lists with as many names as you want.
For more information on versions earlier than Office 2007 SP2, see the Knowledge Base article on the maximum size for distribution lists