Convenience method that provides a quick way to add an email grant
        to a key. This method retrieves the current ACL, creates a new
        grant based on the parameters passed in, adds that grant to the ACL
        and then PUT's the new ACL back to S3.

        :type permission: string
        :param permission: The permission being granted. Should be one of:
                           (READ, WRITE, READ_ACP, WRITE_ACP, FULL_CONTROL).

        :type email_address: string
        :param email_address: The email address associated with the AWS
                              account your are granting the permission to.

        :type recursive: boolean
        :param recursive: A boolean value to controls whether the command
                          will apply the grant to all keys within the bucket
                          or not.  The default value is False.  By passing a
                          True value, the call will iterate through all keys
                          in the bucket and apply the same grant to each key.
                          CAUTION: If you have a lot of keys, this could take
                          a long time!

def add_email_grant(self, permission, email_address, headers=None):
        """
        Convenience method that provides a quick way to add an email grant
        to a key. This method retrieves the current ACL, creates a new
        grant based on the parameters passed in, adds that grant to the ACL
        and then PUT's the new ACL back to S3.

        :type permission: string
        :param permission: The permission being granted. Should be one of:
                           (READ, WRITE, READ_ACP, WRITE_ACP, FULL_CONTROL).

        :type email_address: string
        :param email_address: The email address associated with the AWS
                              account your are granting the permission to.

        :type recursive: boolean
        :param recursive: A boolean value to controls whether the command
                          will apply the grant to all keys within the bucket
                          or not.  The default value is False.  By passing a
                          True value, the call will iterate through all keys
                          in the bucket and apply the same grant to each key.
                          CAUTION: If you have a lot of keys, this could take
                          a long time!
        """
        policy = self.get_acl(headers=headers)
        policy.acl.add_email_grant(permission, email_address)
        self.set_acl(policy, headers=headers)