EDIT 10/27/2009: Please see the updated statement on this subject here.
Please be advised that Single Label Domain (SLD) support in the next version of Exchange is under review.
In February 20...
Updated Jul 01, 2019
Version 2.0
Blog Post
1 MIN READ
Next version of Exchange and Single Label Domain (SLD) policy under review
On the number of SLD, I support about 20 sites and 2 are SLDs. They have generally had Exchange for many years, have one or two servers and don't need or want to go through a major domain restructuring.