NameVirtualHost *:80
ProxyRequests off

ProxyPass / http://www.domainA.com/
ProxyPass / http://www.domainB.com/

<VirtualHost *:80>
    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/html
    ServerName firewall.domainA.com.br
    ErrorLog logs/internal-error_log
    CustomLog logs/internal-access_log common
</VirtualHost>

<VirtualHost *:80>
    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/webmail
    ServerName webmail.domainB.com.br
    ErrorLog logs/external-error_log
    CustomLog logs/external-access_log common
</VirtualHost>