Login to the control panel, click member management, click "All Users" then at the bottom of the search index (After you hit submit) you'll see "all members in search" and a dropdown, now choose that you need to click "mail members" with "all members in search" selectec.

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
Do you need Forum Install or Upgrade Services?
Forums: A Gardeners Forum
UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
Longtime Supporter & Resident Post-A-Holic
VNC Web Services: Code Modifications, Upgrades, Styling, Coding Services, Disaster Recovery, and more!