There is a missing information in english HylaFax wikicontrib:
after hylafax upgrade, you need to change /etc/hylafax/etc/mailfax script, with this new one:
/usr/bin/faxmail -s a4 \
-n -u uucp "$EXT2@`/usr/bin/expr \"$HOST\" : '\(.*\)\.fax$'`" \
"$SENDER"
and then do
chown root:root /etc/hylafax/etc/mailfax
chmod +x /etc/hylafax/etc/mailfax
Leonardo