need some help here.
below is my setup. (replaced actually with dummy names)
I have an mx record going to mail.bfdn.com.
and mail.bfdn.com is an A record to
With main domain bfdn.com.
Doamin registered at godaddy.com. Purchased only a domain only , no email account.

I installed Zimbra Network edition 6.0, all in one linux server.
Sending and receiving internal mail works fine. created multiple account and works fine.

My problems.
1. If i send an email from gmail, it comes back with below error
550 550 #5.1.0 Address rejected
Looks like my zimbra server is rejecting it.

2. I open the webUI of an email account. Tried to compose email to my gmail account, i get
"Invalid address
554 5.7.2 Relay access denied"

How to solve these two problem.
I need to be able send and receive from and to external email accout.
I read setting up a smtp relay host with password but i cant put in password for all 1000 emplyees we will migrate.

Appreciate any help.