Suggest you get an email address not linked to your RSP. If you ever leave Optus they will cancel all your email addresses (you can't take them with you).
It takes about 5 minutes to set up a free GMail account. It has better security, spam filtering and features. And you can use it with any RSP.
I tend to agree with @petergdownload on this one.
If you do want to add an additional email address, we do allow you to add up to 15 email addresses. You will need to contact us and ask us to add the email address.
This functionality is still being fleshed out in My Account (in terms of the integration with our new servicing platform).