Hello,
Adding html should work just fine.
For example my own email template is:
<table style='width:100%' border='0'>
<tbody>
<tr>
<td align='center' valign='middle' style='width:300px;height:94px'>
<img src='https://www.key4ce.com/images/logo.png' alt='Key4ce' width='263' height='62'>
</td>
<td valign='middle' style='width:709px'>
<h1 style='text-align:left'><span style='font-size:large;color:#368caa'> There has been replied to your ticket</span></h1>
</td>
</tr>
</tbody>
</table>
<table style='width:100%' border='0'>
<tbody>
<tr>
<td valign='top' style='width:120px'>
<br>
<br>
</td>
<td valign='top'>
<span style='font-size:10pt;font-family:verdana,geneva'>Dear $username,</span><br>
</td>
</tr>
</tbody>
</table>
<table style='width:100%' border='0'>
<tbody>
<tr>
<td style='text-align:right;width:120px'>
<span style='font-size:10pt;font-family:tahoma,arial,helvetica,sans-serif;color:#888888'><em><strong><br>
Ticket: </strong></em></span>
</td>
<td>
<span style='font-size:10pt;font-family:verdana,geneva'><br>
<a href='$ticketurl' style='color:rgb(84, 141, 212)'>#$ticketid</a></span>
</td>
</tr>
<tr>
<td style='text-align:right;width:120px'>
<span style='font-size:10pt;font-family:tahoma,arial,helvetica,sans-serif;color:#888888'><em><strong>Subject: </strong></em></span>
</td>
<td>
<span style='font-size:10pt;font-family:verdana,geneva'>$ussubject</span>
</td>
</tr>
<tr>
<td style='text-align:right' valign='top'>
<br>
<br>
<span style='font-size:10pt;font-family:tahoma,arial,helvetica,sans-serif;color:#888888'><strong><em>Message: </em></strong></span>
</td>
<td>
<br>
<br>
<span style='font-size:10pt;font-family:verdana,geneva'>$admin_response</span>
</td>
</tr>
<tr>
<td>
</td>
<td>
<br>
<br>
<span style='font-size:10pt'>To respond simply reply to this email or <a href='$ticketurl' style='color:rgb(84, 141, 212)'>click here</a> to make a reply online</span><br>
<br>
<span style='font-size:10pt;font-family:verdana,geneva'>$signature</span><br>
</td>
</tr>
</tbody>
</table>
In the email template: *Admin Response Email
Regards,
Marco