Summary:
Is there some way to guarantee the e-mail sent and received from a specific site or domain is encrypted?

PerfectMail anti-spam is an edge-device supporting TLS encryption, allowing for the sending and receiving of secure data across public networks using the SMTP protocol.

With mail systems, often the option of TLS encryption is present, however plain text transmission exists as a fallback measure when TLS encryption is not available when exchanging e-mail with remote systems. The fallback to plain text data transmissions can be a significant security hole for organizations dealing with sensitive personal or financial information.

PerfectMail gives you the ability to enforce the encryption of e-mail traffic to sensitive locations by offering a Force Encrypt option. With Force Encrypt, e-mail traffic sent or received to specified servers and e-mail domains MUST be encrypted or the e-mail connection is refused, with appropriate notification to the sender.