Your client just wants to send an email
You want to make working together easier to follow, but you know your contact. They do not want another account, another password or another tool to check every day. Sending an email works perfectly well for them already.
That is an understandable starting point. If a new approach only adds more steps, it is hard to keep up. Start with a question your client needed to answer anyway.
Let the email lead to the request
Assign a clear task to your client in trygga. The email contains a link to that task. Your client opens the request without a password and replies there. The instructions and earlier replies are already alongside it.
Notifications about replies are grouped together. Summary emails can also highlight outstanding work and progress. Your client can adjust their email preferences. Explain what the link does for them: answer the question with the background at hand, without creating their own account or remembering a password.
Give the new approach time
Some clients will keep replying by email at first. Add their reply to the right task yourself. This is a deliberate action, not an automatic inbox import. Keep the project up to date so your team can rely on it.
With the next question, you can point to the same place again. Linking each request to the right task helps your client become familiar with the approach without turning it into a training exercise. Read more about access and communication in client collaboration.