Email Sent from Inactive Employee?

Using our info@... email account assigned to a new employee - the email generated substituted the User Name of the previous/inactivated employee.

The inactive employee detail does not even show an email address associated with the inactive employee!

Example:

Inactive Employee/User - Catherine Smith - used to have email address directed for info@... but her Employee account shows no email address and has been blank since November 2005.

Currently Active Employee - Sandy Brown - has email address for info@... and regularly uses this email address without fail. Today, a customer responded to a merged email template where the user name and signature set as <NLUserName> and <NLSignature> but instead of stating Sandy Brown it shows Catherine Smith!