Why should I use a custom domain? – RedTrack

To run high-volume campaigns, we recommend that you use RedTrack's custom tracking domain.

Here are the reasons:

RedTrack users not using a custom domain will be automatically assigned our default tracking domains:http://redtrck1.com, http://rdtrck2.com, http://rdtrck4.com
As we don’t take responsibility for what users run through our default domains, there is a risk that they may potentially get flagged by antivirus software, traffic sources etc.

Please see this article to find out how to set up your custom domain.