"SharePoint provides a feature for users to use different Display Names and Email addresses across the site collections they are members of. This information is cached in the tp_Title and tp_Email columns in the UserInfo table for every site collection in which the user has permissions. The individual user can update their information or the administrator can do it by visiting the siteusrs.aspx page for every site collection. This allows a user to utilize say, different email addresses for alerts on the same SharePoint Virtual Server but in different site collections. One scenario is where I may want to alert myself of changes to content on one site collection using my work email address, while content from another site collection should send alerts to my personal email address.
The problem with this, is that most enterprise customers I have worked with find this feature really annoying :). They prefer the users account display name and email address to be consistent to what the have established in their corporate environment, and it is an administrative nightmare to to update this information across literally 10's of 1000's of site collections. It also confuses users of SharePoint when their information changes (Say a contractor becomes a full time employee, etc). It can also cause administrative headache for administrators when they try to change security information on their sites (in some places we try to look up the account with the old NT Login Name). You can however, re-sync SharePoint with the current information in active directory by using SPUserUtil"
- Using SPUserUtil to synchronize SharePoint user Display Names and Email addresses with the information in Active Directory
Another interesting article of Keith is an earlier article about what to do when the name of a user account changes: