This policy setting controls whether Outlook verifies the user's e-mail address with the address associated with the certificate ...

This policy setting controls whether Outlook verifies the user's e-mail address with the address associated with the certificate used for signing.If you enable this policy setting, users can send messages signed with certificates that do not match their e-mail addresses.If you disable or do not configure this policy setting, Outlook verifies that the user's e-mail address matches the certificate being used for signing.