It is difficult to figure out which options are available via configuration files if they are not explicitly set out.
I would suggest either making a "everything-config-file" or just putting everything in the template file with much commented out.
The two options which I needed and took more than hour to deduce (randomly try different things) were:
<mailet match="All" class="RemoteDelivery">
And then the other option (which I only figured out I needed after watching the java debug stream, (i thought this would be the default))
It would be nice if I could see all of the other option available to me.
(yes I know you are not going to spell out all of the javamail options, but maybe a block like:
Turn on debugging of mail delivery through java mail
Turn on TLS for javamail
Other options for javamail can be specified as