When a recipient receives a Zix secure message, they receive an email that looks like this:
If it is the recipient’s first time opening a Zix secure message, they will need to register their email.
See this article: Registering Zix Secure Message Account
If they have already registered an account, they will need to sign in or recover their password.
After logging in, to open a message, they will need to just click on the message subject.
Do not select the Checkbox to open messages. The Checkbox is used to delete multiple messages.
You can read more here: Registering Your Account (zixhelp.com)