What can someone tell from my email address?

Protect yourself next time

This is a situation that calls for a "throw away" email address.

Before sharing an email address, go create a new one at one of the free email services like Gmail, Hotmail, Yahoo, or others, and give that email address to the person that you're contacting but don't quite trust.

That way, you can give them your "real" email address once they gain your trust, and if they violate your trust, you can simply discard it.

All the while protecting yourself.

Protecting yourself from what?

Spam

As I mentioned above, spam is the most obvious result. It's quite possible, perhaps even likely, that you'll end up getting more spam as a result of sharing your email address with someone who you're not quite sure of.

The interesting thing about using this as a way to harvest email addresses for spamming is that while it seems very labor intensive, the spammer also has a much more targeted idea of what you're interested in, making your email address that much more valuable to them.

Privacy violations

This is a little harder to qualify, because what I'm about to talk about is public information, but do this:

Enter your email address into a search engine or two.

If information about you shows up in the results, then anyone with your email address can perform the same search and get the same information.

This isn't the search engine's fault - they're simply indexing public information on millions of websites and your email address happens to be on some.

If a lot of information about you is public and you've just given your email address to a stalker - well, "privacy violation" doesn't seem like a strong enough statement.

Malware

You asked about malware and data loss. Fortunately, the news here is fairly good in that you are ultimately in control. The bad news is that it doesn't matter what email address that you use.

Let me ask you this: if your new found contact emailed you an attachment, would you open it?

If you answered "yes", then you could have just accepted and installed malware on your machine that could wipe it out, steal your account password(s), or who knows what else.

In other words, you are definitely at risk if you aren't paying attention.

I'd also be extremely wary of even visiting websites that you don't recognize that are suggested by this person for exactly the same reasons.

Politely decline 'em all. If the person is legitimate, they'll understand. If they insist, get angry, or threaten to leave, then that's a sign that perhaps all isn't what it seems (or that they need to read this article).

Making contact over the internet

The advice here really applies to more than just dating sites.

Any contact that you make that is initially and only over the internet entails a certain amount of risk. The person may not be who they say they are. They may have malicious intentions. Until you can build a sufficient level of objective trust, it's best to avoid sharing your "real" email address and view everything with a healthy dose of skepticism.