I had some questions before installing Zimbra. I hope you can forgive any dumb questions. But, I figure dumb questions are better than smart mistakes.

Right now my company gets our web mail through our web host via a POP session & Thunderbird.

I'd like to try Zimbra without affecting our existing setup.
Can I just test it out with a few users or do I have to switch everything over?
Is there anything required like editing the MX Records?
My ideal situation is the ability to have Zimbra send/receive emails, but leave them on the server, where we can download the mail on our existing e-mail clients.

I'm fairly new to Linux (switched to Ubuntu about 3 months ago & love it)
It would be nice just to click on Synaptic Package Manager and install Zimbra
through there. The Ubuntu install guides I've seen have me making changes to the MX Records and everything.
I just don't want to get myself in trouble and have 30 people who can't get their email, because I'm trying stuff out