To try and fix the issue with sending attachments via Outlook, please consider the following steps:

1. Check the size of your attachment: Microsoft Outlook has a default attachment file size limit of 20MB and some emails may reject attachments larger than this. Try sending a smaller file or splitting the attachment content to multiple emails.
2. Check your internet connection: Having a poor or an interrupted internet connection can also be an issue for failing to send an attachment.
3. Check for compatibility problems: Ensure that the file you're sending is compatible with the recipient's email client. Some rare file extensions may not be supported.
4. Disable proxy settings: Outlook can fail to send attachments if there are proxy settings enabled, so try disabling them to see if this solves the issue.
5. Configure Windows Firewall: If you're using Windows Firewall, try temporarily disabling it and see if that helps.
6. Repair Outlook: If none of the above helped, then one alternative could be to repair Outlook to fix any corruption or misconfiguration.