Start Your Own Safelist
Are you ready to start your own opt-in safelist?
There's a lot to consider. Are you going to install a script yourself? Or are you going to buy a ready hosted script, that will be installed for you? You even have the choice of adopting a safelist.
You will need to think about the price of course. You will also need to think about how complicated a script, that your skills can handle. Then there's the web-host to consider.
Some hosts have good reputations; some don't. Some scripts run fine,; other scripts have their little bugs.
Bellow are mainly known safelist hosts, but there's a couple of good scripts as well.
PERSONAL NOTE: I have been objective here, not everything here is 100% recommended. Purely honest information to the best of my knowledge. There is a lot more to think about too. This would be a great place to start your reasearch.

