What is Reverse DNS, and do most hosts have this set up?

I'm asking because some people here say that you can have email problems if your host doesn't have reverse dns set up.

Please explain.

Reverse DNS is mapping an IP address to a host name as opposed to mapping a host name to an IP address. Unless your provider has delegated reverse DNS authority to you, which very few providers seem to be willing to do, you will have to contact your provider to have reverse DNS setup, and they may even have to contact their provider as well. You will have to tell your provider what host name you want the IP address to resolve to. Some mail servers will reject mail from a mail server without reverse DNS.

thanks, Toasty. I'm confused tho' by your use of the term "provider". By "provider", do you mean the host, ISP or bandwidth provider?

If you have a dedicated server, your provider is where you are renting the dedicated server from.

Provider reffers to everyone...

Provider would be the people who own your dedicated server, and Provider would be the person providing the fiber, like UUnet, Cogent, Sprint, Yipes..