Thank you for posting the query on Microsoft Community. I am sorry to know that you are facing issues with Outlook.com
How are you trying to access Outlook.com? Is it through Web or App?
Is the issue confined with one particular sender/domain or with anyone?
Is the attachment size more than 10 Mb?
Please be informed, if you send an email that exceeds the maximum email size limit of the recipient’s email provider, your email will bounce off and you will receive an email error back in your mailbox. Usually, you will receive one
of the following error messages: