Which Secure Delivery Mode is not available with Mimecast?

The correct response identifies the Secure Delivery Mode that is not offered by Mimecast as the Default / Opportunistic mode. Mimecast focuses on providing robust email security by enforcing secure protocols. This approach enhances the overall integrity and confidentiality of email communications.

Default or Opportunistic modes typically allow for sending emails without enforcing a particular transport security security protocol, which could lead to a less secure message delivery process. In contrast, Mimecast prioritizes security measures such as enforced TLS, which mandates that email communications must use secure connections, and X-Enforced TLS, which then fall back on secure messaging if a secure connection cannot be established.

By not supporting Default / Opportunistic mode, Mimecast ensures higher security standards, reducing the risk of data breaches or interception during email transmission. This commitment to security makes other modes that involve stricter protocols the logical options in Mimecast’s suite, reinforcing the company's dedication to protecting email data effectively.