The upstream Mail::DMARC ships its own copy of the public-suffix data
and references this copy in the example mail-dmarc.ini file.  In
Debian, the public-suffix list content is available in
/usr/share/publicsuffix/public_suffix_list.dat as provided by the
publicsuffix package.

If you wish to use a private copy of the publicsuffix data, edit
mail-dmarc.ini and specify its location in the dns.public_suffix_list
field.
