XMPP switches on mandatory encryption

If you're using a dedicated OVH server, why are you using their DNS? In my experience, OVH give you cheap, well-connected and reasonably reliable servers (in the sense that they get replaced quickly when they break, I hope you had backups), but their services are not very useful -- they probably expect you to roll your own.

So apt-get install bind, point your NS at your server, and be done with it. I don't recall if OVH are willing to act as secondary, but for most applications secondaries are not really a hard requirement (and if you really need a secondary, you'll want it to be somewhere else than on OVH's network).

(I'm more annoyed about their IPv6 infrastructure -- a single /64 per server that is not routed, so you need to proxy-ND in order to do anything out of the ordinary.)