Q: Is it okay to have multiple domains pointing at my website? Will I get penalized for having duplicate content?

A: To answer your first question, yes. As a matter of fact, there are lots of good reasons to have secondary domain names. Running a TV ad? Print a special domain URL to track where visitors came from. Airing a radio ad? Use a name — maybe even a phrase — that's memorable and easy to spell. (By the way, in those cases I wouldn't advise using a TLD extension other than .com.)

But are you asking because you registered a bunch of keyword-rich domain names for SEO purposes? Sorry to be the bearer of bad news, but these domains are NOT your ticket to great search engine positioning!

In answer to your other question, not exactly. The search engines don't penalize dups. They just filter them out, which makes a great deal of sense if you think about the enormity of their job of attempting to index the entire Internet! (Read a great explanation of that here.)

Be sure to designate just one primary domain for your website. You can point unlimited secondary domains at the primary one and never have to worry about confusing the engines.

The key is to make sure the address bar shows the primary domain name no matter what domain name was used to bring the visitor there. In other words, DON'T "mask" the primary name.

I had to learn this the hard way.

I ran into some trouble a few years ago with one of my sites. There is a common misspelling so naturally I registered that domain as well and had my web host "park" it on top of the main domain. Parking, unfortunately, masks the domain name in the address bar. Google wound up indexing half of my pages under the misspelled name.

There are three ways the major search engines like to find out about a new site:

1. By following a link from another site

2. By "spying" on users who have the engine's toolbar installed

3. By mining the domain registry for new registrations. In their 2005 patent application, Google hinted about doing this. Now, Google doesn't usually add a site that doesn't have incoming links nowadays, but I don't know what the policy is on the other engines.

* * *

So Google either found a misspelled link somewhere on the Net or — more likely — someone who had the Google toolbar installed misspelled the domain name when typing it. Google then indexed every page the misspeller visited — under the misspelled domain name instead of the correct name! Naturally, this presents a fractured view of the site. Google didn't know I had tons of great content on ONE site, because it saw this as TWO separate sites. Since "content is king" that was not a good thing.

To solve the problem without upgrading to full hosting for the secondary domain, I unparked it and started using my registrar's forwarding service — specifying no masking.  I chose the "301" (permanent redirect) rather than the "302" (temporary redirect) status.  Some registrars charge for forwarding, but probably less than it would cost for hosting. If you're already paying for hosting anyway, just ask your host about setting up the 301 redirect from the htaccess file.

I still have to check periodically to be sure other sites are linking to the correct version of the name.

The PageRank (PR) number did get upgraded after this was done and the wrongfully indexed pages were deleted on Gpogle's next crawl.

I don't think that PR is as important as people think it is, but I do believe that when the search engines accidentally index individual pages of one site under secondary domain names, you don't get credit for the full depth of the site. So play it safe if you want more than one domain name for your website, and make sure each is set up with a 301 redirect.