**On Centos**
You can change php70 with your PHP version of choice
yum install epel-release
yum install gcc plesk-php70-devel zlib-devel
/opt/plesk/php/7.0/bin/pecl install mailparse
echo "extension=mailparse.so" > /opt/plesk/php/7.0/etc/php.d/mailparse.ini
To confirm if Mailparse is installed use
/opt/plesk/php/7.0/bin/php -m | grep mailparse
mailparse