The most common cause is a broken or too full Outlook cache, with other reasons including wrong mailbox time zone settings or turned-off add-ins. In some cases, Protected View rules or limits on temporary file access can also stop attachments from opening.
1. Check for Internet Connectivity
If your internet connection is slow or unstable, the attachment may not load and open. Try switching to a different network or to the 5 GHz band on your Wi‑Fi for faster speeds. You can also restart your router. Press the power button on the back of the router to turn it off, wait a few seconds, and turn it back on. Once it restarts, check if your internet is stable. If possible, use an Ethernet cable instead of Wi‑Fi. A wired connection is usually more stable and can prevent interruptions.
2. Check for Compatibility Issues
You may not be able to open an attachment in Microsoft Outlook if the file type isn’t recognized by your computer. Ask the sender to resend the attachment in a common format your apps can open (for example, PDF, DOCX, XLSX, JPG, or PNG).
3. Make Outlook Email Address As Primary Email Address
If you have multiple accounts in Outlook, set the account you use to receive the attachment as the default.
4. Clean Outlook Cache Files
Sometimes Outlook’s cache gets corrupted and causes issues with opening attachments.
5. Update Microsoft Outlook
If Outlook won’t open attachments, you might be missing important updates. Updating Outlook can improve stability, security, and fix bugs that cause this issue.
6. Disable Outlook Add-Ins
Some Outlook add-ins can conflict with attachments. Disable them one by one to find the culprit.
7. Disable Antivirus Software
Antivirus software can sometimes flag safe files by mistake and block them. If you still can’t open attachments, your antivirus might be interfering with Outlook. Temporarily turn off your antivirus and try again. Remember to turn it back on afterward.
7.1 Microsoft Defender
7.2 Third-party virus protection:
8. Check Outlook Attachment Handling Settings
If attachment preview is turned off, you might not be able to open attachments directly in Outlook. Reboot Microsoft Outlook and try to open the attachment to see if the problem is fixed or not.
9. Run scanpst.exe Tool
If the issue persists, run Outlook’s built-in Inbox Repair Tool (scanpst.exe). It can repair corrupted Outlook Data (.ost) and Personal Folders (.pst) files.
