Hi Franklin,
Which type of email account are you using? IMAP, POP3 or Exchange?
Do you mean the attachments can't be seen in the replied/updated emails or the original emails?
If it's the former, please check Ashish's suggestion and take the action to fix the issue. By default, Outlook does not include attachments when you reply to a message.
If it's the latter, we may first try to clear the Outlook Secure Temporary File and then test the issue again. To do this, please follow:
1. Open Registry Editor and navigate to:
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security
2. Open the OutlookSecureTempFolder registry key and copy the path from the key value.
3. Open Explorer and paste the copied path in the Address field, press Enter.
4. Clear everything in folder.
5. Restart Outlook and then test the issue again.
Since the attachments are stored in Outlook data file, if above doesn't help, we can also try repairing the data file to see the result. See:
https://support.office.com/en-us/article/Repair-Outlook-Data-Files-pst-and-ost--25663BC3-11EC-4412-86C4-60458AFC5253?ui=en-US&rs=en-US&ad=US
Hope this helps.
Regards,
Steve Fan
TechNet Community Support