People familiar with the upcoming beta told AppleInsider that the email was sent out to members of AppleSeed, the group of developers selected to test Apple's next Mac update, and said the invites the company sent out last month were "too early."
From the email:
Thanks for accepting our invitation to test OS X Mountain Lion 10.8.3. The invites were sent out a little too early! We are working hard to provide you with a seed build soon, but we wanted to let you know that you have not missed any seed announcements. Please enjoy the USA Thanksgiving holiday! The Seed Team will be enjoying a break as well. Look for more information about the 10.8.3 seed during the week of November 26th.
Thanks for your patience!
AppleSeed participants began receiving invites on Oct. 31, signaling that a beta for the next version of Mountain Lion was nearing completion. In the past, AppleSeed members have receive builds of new Mac versions alongside registered OS X developers.
The most recent Mountain Lion update came in September when OS X 10.8.2 was released, bringing system-wide Facebook integration and other features.