...
${recipient}: Recipient name.
${issueKey}:Issue key.
${issueSummary}: Issue summary.
${issueLink}: Issue link. (Ex: <a th:href="${issueLink}" th:text="${issueKey}"></a>).
${ratingSection}: Rating section in email. It can be emoticons, stars or numbers. You can change rating type in General tab.
Elements: div, span, a, img.
Attributes of elements: align, style, th:text, th:href, th:src.
For example:
<div align="center" style="padding:10px"/>
Hi <span th:text="Admin"></span>,
<img th:src="@{https://genk.mediacdn.vn/2017/google-1491681053193.jpg}" />
Important note: Don’t forget to add ${ratingSection} variable to the template.
...