Hi @Iniobong Nkanga ,
To deal with the current situation, you can refer to the methods in the document shared by Dave to help trim the size of this user's mailbox.
Or as an Exchange administrator, you can increase the mailbox quota for this user, by following the document below, suppose your organization is using Exchange Online:
Increase or customize Exchange Online mailbox size
Please how to do i prevent this issue.
- From the perspective of end-user side, I'd recommend sharing the best practices in the link provided by Dave to keep the mailbox size under control:
- Archive older items
- Empty the Deleted Items folder
- Empty the Junk Email folder
- Store attachments outside your mailbox
- From the perspective of the Exchange administrator side, you can enable the archiving for the mailbox and create retention policies against the Exchange mailboxes to retain and delete mails automatically. Some documents for reference:
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