Okay, so ZCS has support to poll external POP accounts.
Say I have ZCS on mail.foo.com. I have also three accounts on gmail.com, firstname.lastname@example.org, email@example.com and firstname.lastname@example.org. I have ZCS email acc email@example.com
I check my external pop accs every 5 minutes. I get an email in firstname.lastname@example.org. I reply, and.. by default it will of course send using ZCS MTA and will have From: email@example.com.
Can I set up external SMTP servers just like POP so I can use them as well. (ie. Groupwise let's you do that). I'm migrating from Groupwise so I have to have that.