Left column below shows the name of the placeholder, right column shows an example value of this variable. Once the placeholder from left is added to the e-mail template, the placeholder will be replaced with the right value in the e-mail.
For example: In the case of "policy_no": "P2018020018" you should write {policy_no} to the e-mail template. In the sent e-mail the [policy_no} will be replaced with P2018020018.
Additionally, it is possible to write {customer_name|Customer}. In this case the text will be added as: Customer John Cover. In cases where customer_name value is empty, nothing will be shown.
Please note that placeholders are specific to the email context (e.g there are generic customer placeholders and others that relate to invoices)