Using Outlook for Android in business environments for email and scheduling
Hello Gemma! Welcome to the Microsoft Community for asking your question.
If either your Outlook.com mailbox or your OneDrive storage is full, you cannot send or receive new emails and will receive that message. check your OneDrive storage on the link below to see how much space you have.
Your OneDrive storage is different from your email storage.
I recommend you use a laptop and web browser in order to see your OneDrive storage.
Outlook Storage
https://outlook.live.com/mail/0/options/general...
How does Microsoft storage work?
https://support.microsoft.com/en-us/office/how-...
To know more, about "changes to Microsoft 365 email features and storage"
https://support.microsoft.com/en-us/office/chan...
Please let me know for further assistance.
Best,
Janbaz