If PHP 7.1 fails to build on a Directadmin server with the error saying "libtool: link: `ext/gd/gd.lo' is not a valid libtool object" here you can find a possible solution, which worked for us and may work for you.
If emails on your Directadmin server stopped delivering to your users, and the error "550 Email blocked by combined.rbl.msrbl.net" is reported, here is what you should do.