When using the UserManager API to update a users's email address to an address containing a Top Level Domain (TDL) that is longer than 5 characters you receive and "invalid email address" error.
This is a known limitation of the email validation check in Ektron versions prior to 9.0. In older versions the validation checked that the TDL was between 2 and 5 characters. This length restriction was removed in Ektron 9.0 to allow the validation to work with new and feature TDLs. In order to use the UserManager API with a longer TDL email address you will need to upgrade to at least Ektron 9.0, use the older Ektron.CMS.API interface to update the email, or update the email address one at a time via the WorkArea.
It is highly recommended to upgrade as the old API interface is depreciated and upgrading to the new versions of Ektron will get you more bug fixes, security patches, performance improvements, and much more.