Here are some posts related to Zimbra mail server's ports and configuration:

• Zimbra Firewall Configuration
• ZimbraApache
• Performance Tuning Guidelines for Large Deployments
• Howto: Bind to one specific IP / Listen to one IP
• Zimbra 5.0 RC1 http jetty binding to IP on Server to multiple IPs

To change Zimbra apache port 80 and 443 to something else, do the following (with the appropriate SERVERNAME):

su - zimbra
zmprov ms SERVERNAME zimbraMailPort 81
zmprov ms SERVERNAME zimbraMailSSLPort 444