Can you do this by the guidelines of Yahoo Answers?

I don't think it's against the guidelines, but a better way would be to simply tell them to email you when you answer, and point the way to your profile. Yahoo! has made it very convenient to all by letting you have three settings for your contact info: Hide, Display, and Allow Contact Without Actual Concrete Information. You can make it so that people can email/IM you without actually knowing your email address.

First of all, I wouldn't recommend this regardless of the guidelines. There are some very strange people out there, you should really be careful. It's good that you like to help but be cautious. Have you considered your own web page dedicated to helping others through Q@A?

well, i'm not sure it follows the guidelines, but when people seem like they need to talk, i tell them they could message me if they want, i have the links open on my profile for that, the people who me are the ones who want help, but are afraid to seek it with somebody they actually know, or who could talk to people they know, it even helps me in a way, it gives me something to be proud of, that i am helping people, i may not know them, but the knowledge that i was able to improve their life just a tiny bit, makes me feel better about myself, instead of making me feel like just something that is there and a piece of garbage, which is what my family, my mom especially, tells me all the time

I see people do it all the time so I don't think it is

I do It all the time and I've never been pointed out or warned by it.

-coffee