Optus email is a "best effort" service, it's a freebie add-on that many ISPs are starting to ditch because of the huge amount of spam that occurs (with people having insecure computers spamming etc).
Could you be more specific to "slow"?
Are you saying, the email takes too long to come in? If its "too long", how long is it actually taking? And what timeline are you expecting for a free service?
Are you saying pages load slowly?
My husband forwarded an email to me and it took more than 1/2 hour to reach me. We were both at home at the time. Yesterday an insurance lady sent me info and a quote. She sent it while we were talking yet it also took about 1/2 hour to reach me. Emails from 'StarNow' with modelling and acting jobs don't show up when normally I would see them almost straight away. Now I go to the website as otherwise I might miss jobs. Btw, what other options are there? I also have a Gmail account but hardly use it. I use my PC for opening email and it goes through OUtlook. But...even when I open up Optus Webmail it does not seem to make a difference.
You can get GMAIL through "Outlook".
The issue of "emails actually" arriving will be the same between Outlook and/or Webmail. You need to remember that it has to go through multiple spam filters before it reaches your actual "inbox" that both webmail/Outlook can see.