Sender identities are tightly integrated with external profiles that
you configure on Convergence to collect emails from other accounts. When
you set Convergence to collect email from external accounts, an identity
is created for you and is added under the Identities node in the Mail
preferences. The identity is removed when you delete the account setting
for collecting external mail. See How do I Remove an Existing
External Account?
Note - The default identity cannot be removed.