These experiments leave me with the following questions/comments.
I am under the impression that the MAILTOURL is only applied
withing the formatting of message headers which must appear prior
to the formatting of the message body. So far as I understand
the documentation, I do not have access to an URLencoded copy of
$SUBJECT$, outside of the application of MAILTOURL in the course
of header processing.
Use the ":U" modifier. Ie. To get a URL encoded version
of a message's subject, use the following: $SUBJECTNA:U$
If I am mis-reading the documents, or if one can do more than the
documents say, I would like to know, because I would prefer to
suppress the header formatting entirely and write my own links
below the message body, including mailto's with the above classes
of parameters. So far I haven't devised a method to get the full
mailto: I want without leaving the headers in.
An example of adding a mailto link of your own:
(The newlines are for readability only).