Sending, receiving, and organizing email in Outlook.com
I understand how disruptive this can be, especially when it is affecting your bookkeeping workflow.
Based on your description, Outlook.com may be blocking the Sage backup file because its file extension is classified as a potentially unsafe attachment type. Outlook blocks certain file types from being sent or received to help protect users from malware and other security risks.
Could you please let me know the exact file extension of the backup file (for example,.001,.cab,.zip,.ptb, or another extension) and the exact warning message you receive?
Meanwhile, if this is a Sage backup file type that Outlook.com considers unsafe, you can try one of the following workarounds:
- Upload the backup file to OneDrive and send your accountant a sharing link instead of attaching the file directly. Microsoft recommends this approach for blocked attachment types.
- Compress the backup file into a.zip file and then attach the ZIP file to the email. Outlook may allow the compressed file if the original attachment type is being blocked.
- If appropriate for your workflow, rename the file extension before sending, then have the recipient rename it back after downloading. Microsoft lists this as another supported workaround for blocked attachment types.
For more information, please see Microsoft's article: Blocked attachments in Outlook: Microsoft Support - Blocked attachments in Outlook