Custom E-mail notification

Which email do you mean? For example, the emails sent by process model alerts cannot be customized.

Are you talking about email sent from Send email Node in process?

{
  a!localVariables(
    local!rows: a!forEach(
      items: enumerate(50) + 1,
      expression: {
        id: fv!item,
        selected: false,
        value: "Value " & fv!item
      }
    ),
    a!formLayout(
      label: "Editable Grid with Checkboxes",
      contents: {
        a!gridLayout(
          label: "Grid",
          data: local!rows,
          columns: {
            a!gridColumn(
              label: "Select",
              value: a!checkboxField(
                label: "",
                labelPosition: "COLLAPSED",
                value: a!forEach(
                  items: local!rows,
                  expression: fv!item.selected
                ),
                saveInto: a!forEach(
                  items: local!rows,
                  expression: a!save(
                    local!rows[fv!index].selected,
                    fv!value
                  )
                )
              )
            ),
            a!gridColumn(
              label: "ID",
              value: a!textField(
                label: "",
                labelPosition: "COLLAPSED",
                readOnly: true,
                value: a!forEach(
                  items: local!rows,
                  expression: fv!item.id
                )
              )
            ),
            a!gridColumn(
              label: "Value",
              value: a!textField(
                label: "",
                labelPosition: "COLLAPSED",
                value: a!forEach(
                  items: local!rows,
                  expression: fv!item.value
                ),
                saveInto: a!forEach(
                  items: local!rows,
                  expression: a!save(
                    local!rows[fv!index].value,
                    fv!value
                  )
                )
              )
            )
          }
        )
      },
      buttons: a!buttonLayout(
        primaryButtons: {
          a!buttonWidget(
            label: "Submit",
            submit: true,
            style: "PRIMARY"
          )
        }
      )
    )
  )
}