As documented, when you want to use an ampersand in a template, you
have to double it.  Thus

"Magic Commands":
to stop receiving mail for awhile, click here and send the email:
mailto:[log in to unmask]&&body=SET%20IRWOLF-L%20NOMA
IL

to restart your mail click here and send it:
mailto:[log in to unmask]&&body=SET%20IRWOLF-L%20MAIL

Frankly I would get rid of the subject, LISTSERV doesn't need it (and then
you don't need the ampersand to begin with).

Nathan