Hey @Rachel924, it sounds like you may have exceeded your webmail quota. I recommend looking through the various webmail folders (Inbox, Sent Mail, Spam) and delete any items you no longer need. You'll then need to also clear the Trash folder after clearing those items.
Once you've cleared out those folders, you'll have more room in your quota to send/receive emails. Please give that a try and see how you go.
If you experience any further issues, I recommend sending us a message via the My Optus App so we can take a closer look at your webmail account for you.
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