Users clicking on campaign links are currently being presented with an unresolvable domain page. Please note that campaigns are still being tracked if the link is clicked on by a user.
This KBA has been published and will be updated when more information is available.
Apologies for any inconveniences caused.
The "unresolved" Phish Threat domain pages were caused by the hosting provider automatically identifying the domains as phishing and, as such, took them offline. These have now been unblocked and we are in discussions with the hosting provider to prevent this from happening again.
In many cases, normal operations has now resumed. Please be aware that the complete DNS propagation may take up to 48 hours.
More info here.