Specifying how user names are recorded
For file and personal geodatabases edited with ArcGIS for Desktop clients, and ArcSDE geodatabases you connect to through operating system authentication, the user name written is the operating system login. The value used is set by the text typed by the user when he or she logs in. If he logs in as John, John writes as the user name. If the next day he logs in as john, john writes as the user name.
For ArcSDE geodatabases you connect to through database authentication, the user name is the name you use to connect to the geodatabase.
If your data resides in an ArcSDE geodatabase and you connect through database authentication, you can choose to append a realm (for example: @esri.com) to the name of the user who makes the edit. For example, if you have a user named John in your Denver office and a user named John in your Seattle office, you can track their edits as John@denver and John@seattle, respectively, so that you can be certain which John made each edit.
To set the realm for an ArcSDE geodatabase, you must have administrator privileges on the database. In the Catalog window, right-click the connection to the geodatabase, click Properties, and click the Editor Tracking tab. You can then choose whether to use the default realm or apply your own.
You can also choose to append a realm to edits made through a feature service. For more information, see Editor tracking for feature services.
Have a look at the below link:
About tracking an editor's changes to data