Hi @Glenn Maxwell ,
Welcome to our forum!
Does this issue occur recently? If so, have you done any specific operations before that?
And do you open several .pst files in Outlook or have a lot of public folders?
If so, please refer to this official article: You receive insufficient memory errors when you expand a mailbox or public folder in Outlook.
In addition, it's suggested that you could reduce the size of your mailbox to check if there're any differences.
Hope to help you!
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