Microsoft acknowledged on Tuesday that fewer than 1 percent of Hotmail customers have thus far been upgraded to the new service, though it said that it plans to add more users this week.
In a blog post, Mike Schackwitz said that as is often the case, Microsoft found a few issues as it started deploying the upgrade. With some minor changes made "under the hood" Schackwitz said the company is ready to put the new Hotmail on a few more server customers.
"When we roll out new software, we typically find a few things that we want to tweak before going out more broadly," Schackwitz said. "Most of these things are actually invisible to our customers--they usually have to do with our ability to monitor the site or make the rollout itself go more smoothly."
Microsoft began the public rollout of the new Hotmail two weeks ago, starting with a single server cluster. So far, a few million people are running the new version, though that is still less than 1 percent of all Hotmail users.
The upgrade, the biggest since Microsoft completely overhauled the Web e-mail service four years ago, adds a number of features, including conversation threading, support for larger attachments, and improved views when opening attachments.
Microsoft said it hopes it will now be able to speed up the pace of adding server clusters to the new Hotmail, but Schackwitz said that it will still be some time before all users are on the new Hotmail.
"We have hundreds of clusters and we want to make sure everything goes smoothly, so it will still take a few weeks to finish," Schackwitz said.