In order to secure business communication with Alcatel based on e-mail, you need to trust the Alcatel Secure Key Infrastructure.

Depending on your configuration, this can be done by registering the Alcatel Authority's certificates into your browser, mail client or operating system. Don’t forget to grant the relevant trust level for each type of certificates. For secure email, you'll need to download the Alcatel Root CA and the Alcatel Internal CA certificates.

Another way to get these certificates is to accept & trust them all, the first time you receive a signed email from an Alcatel counterpart that you know and trust.