Please consider the following patch to make the Appender work in a restricted
sandbox environment.

84,87c84,92
<     Properties props = new Properties (System.getProperties());
<     if (smtpHost != null)
<       props.put("mail.smtp.host", smtpHost);
< 
---
>     Properties props = null;
>     try {
>       props = new Properties (System.getProperties());
>       if (smtpHost != null)
>         props.put("mail.smtp.host", smtpHost);
>     } catch(SecurityException se) {
>         props = new Properties();
>         props.put("mail.smtp.host", smtpHost);
>     }