Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Dear Peter Kingshott,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Based on your description, I understand that you have a concern with "System Administrator notification:" before we proceed, we need more detailed information about the situation you are experiencing.
This issue occurs when any of these conditions is met: The organization's default public folder post quota (DefaultPublicFolderProhibitPostQuota) has been reached, the individual public folder post quota (PublicFolderProhibitPostQuota) has been reached or The Content Public Folder mailbox hosting the mail-enabled public folder has reached its quota.
To confirm this check individual public folder quota and check the content public folder mailbox quota then apply fixes accordingly as in Error (554 5.2.2 mailbox full) when sending email to mail-enabled public folders in Microsoft 365 - Exchange | Microsoft Learn
Please help us in isolating the issue by providing the following information:
- Is the recipient internal or external?
- Since you deleting many emails from account and still does not work, it may be the sending limit, have you tried updating the Send & Receive Limit of the mailbox? See Changes in message store and throttling for concurrent connections - Exchange | Microsoft Learn
If the recipient is outside of your organization, contact them directly and provide the bounce back message to their mail administrator, since the issue may be on their end.
We look forward to hearing from you, please let me know and provide a more detailed description so we can provide you with more specific assistance. Thank you for your cooperation.
Sincerely,
De Paul | Microsoft Community Moderator