I bought a LINUX Appliance a couple years back and it came with Zimbra, cool mail app, the vendor promptly went out of business and left us high and dry and I am by no means a LINUX GURU

We changed from AT&T to Comcast got all new IP's, and now cannot send mail.

My DNS is with Network Solutions and the DNS has been changed. but still cannot send or recieve mail, actually it goes as far as clients using the outside address cannot do SMTP/POP3 or IMAP now either. Using The inside address you can at least connect and send mail, and it gets delivered.

Does Zimbra use its own SMTP server or Sendmail?

There must be some where on the box I have to tell it what the new IP is other than IFCONFIG