can I use the email of the main domain

Here's my setup:

- I have my domain registered at 1and1.com
- I have hosting with Hostgator

I want to continue using my email address as set up on the main domain: myname@joejacobson.com

So when a new user creates a site on my multi-site, what are the ways for them to keep their email (myname@joejacobson.com)? I know there is the domain mapping plugin, which I don't have set up yet.

When I set up this plugin, will the user still be able to use their primary email as setup on their domain registrant?

In the meantime, before I set up the domain mapping, can I do it this way:
1. Do a simple redirect of their domain name to my network (newuser.mynetwork.com)?
2. When I do this redirect, they will be able continue to use their primary email already set up, right?

I just want to be able to do the simple fix now until I can learn how to handle the domain mapping and the mail configuration later.

Thanks, Joe.