For emails scheduled in the cadence after the first step, you can select this option if you’d like to include the previous email in this email’s thread.

This setting is helpful because it gives prospects enough context for your message.

If you have multiple follow-up steps in the cadence, you can select which of the previous emails you’d like to include in the thread.

You can enable this option from Step Settings > Email Thread.

Note: This option is available only in the follow-up email steps and not in the first email step of the cadence

You can also check the box "Use the same subject line" if you want the same subject line in your follow-ups as that of the first email.