Each type of iSAT mailbox comes with a certain number of free email addresses (i.e. joe@domain.com). You can increase the number of addresses at a cost of R5 each. There is however a limit to the number of email addresses you can add to each Mail Option. In other words, if you have the Mail A option, but need 7 email addresses, you will have to upgrade to the Mail B option.
If you have a Mail C option account and wish to make use of more than 50 addresses, you can acquire a second mailbox. See the tables above for more information.