I recently had a subscriber of mine following some training I did a while back, but he had his hosting account instantly banned for using single-opt in.
I thought... that's odd, because there's well over 50% using single opt-ins these days, and probably even higher from us IM guys.
I thought I'd speak to their support and see what they say...
Read Here: Screenshot by Lightshot
Email Policy - HostGator (Number 3 of the Mailing Rules)
So for those of you who are with HostGator... watch your back and make a back-up of everything because who knows when it's going to happen. I have a couple of sites on HostGator but my primary ones are now with someone else luckily.