What triggers Outlook error 17099 on Mac? In documented cases, the error appears when an email with an attachment refuses to send, and the cause is a conflict with the Vulnerability Protection module in Norton Security for Mac. This guide shows how to confirm that trigger and clear the error so the message goes out.
Key Takeaways
- Error -17099 (sometimes shown as -3253) appears when sending an email with an attachment in Outlook for Microsoft 365 for Mac or Outlook 2019 for Mac.
- The documented trigger is the Vulnerability Protection module in Norton Security for Mac version 8.6.3 or newer.
- Norton released a hotfix, so installing the latest Norton updates is the fix.
- Sending a test message without an attachment helps confirm the pattern quickly.
How to Find What Triggers Outlook Error 17099 on Mac and Fix It
The key is to confirm the pattern first, then update the security software involved. Think of it like a smoke alarm that keeps going off: before replacing anything, it helps to know exactly what sets it off.
Confirm the Trigger
- Step 1: Read the error carefully when the send fails. The code to look for is -17099 or -3253, and the email fails to send.
- Step 2: Note whether the message has an attachment. The documented issue occurs when sending an email with an attachment, so a message that fails only when a file is attached fits the pattern.
- Step 3: Send a short test message with no attachment to yourself. If it goes through while the attachment version fails, the attachment send is the problem area.
- Step 4: Check whether Norton Security for Mac is installed on the Mac. Open the Norton app and look at the version number in its About window. Version 8.6.3 or newer is the range tied to this error.
Tip: Test with a small file first, such as a short text document. It keeps the check quick and shows that the error follows attachments rather than one specific file.
Apply the Fix
- Step 5: Open Norton and run LiveUpdate so the latest Norton updates are installed. Norton released a hotfix for this exact issue, and the update brings it in.
- Step 6: Quit Outlook completely by choosing Outlook, then Quit Outlook, from the menu bar.
- Step 7: Restart the Mac from the Apple menu so the updated Norton components load cleanly.
- Step 8: Open Outlook, create the email again, attach the file, and click Send.
Tip: Wait until Norton finishes its update before restarting. Restarting in the middle of an update can leave the old component in place, and the error may come right back.
Common Problems and Fixes
The Error Still Appears After Updating Norton
Restart the Mac once more and confirm the Norton version number has changed. If the update did not install, run LiveUpdate again and let it finish fully before sending the attachment.
The Message Sends Without an Attachment but Not With One
This matches the documented pattern. Check the Norton version and apply the latest Norton updates as described in Step 5.
Norton Is Not Installed on the Mac
The documented trigger for this error is Norton Security for Mac. If Norton is not present, make sure Outlook is current by choosing Help, then Check for Updates, in Outlook. If the error continues, the Microsoft article on this issue and the Outlook community are the best places to report the details.
Error -3253 Appears Instead of -17099
Both codes are listed together for the same issue, so the same steps apply. Confirm the attachment pattern and update Norton.
The official Microsoft article on this issue is available here: Error -17099 or -3253 when trying to send an email with an attachment.
Frequently Asked Questions
What does error 17099 mean in Outlook for Mac?
Error -17099 means an email with an attachment failed to send in Outlook for Microsoft 365 for Mac or Outlook 2019 for Mac.
What triggers Outlook error 17099 on Mac?
The documented trigger is the Vulnerability Protection module in Norton Security for Mac version 8.6.3 or newer.
Is error -3253 the same as error -17099?
Both codes are documented together as one issue that occurs when sending an email with an attachment, so the same cause and fix apply.
Which Outlook versions are affected?
The issue is listed for Outlook for Microsoft 365 for Mac and Outlook 2019 for Mac.
Has this issue been fixed?
Yes. The issue is marked as fixed, and Norton released a hotfix that resolves it.
Do I need to uninstall Norton to fix error 17099?
No uninstall is described in the documented fix. Updating Norton to the version that includes the hotfix is the solution.
How can I tell if Norton is causing the error?
Check whether Norton Security for Mac version 8.6.3 or newer is installed and whether the error appears only when a message has an attachment. That combination matches the documented trigger.
Why does the error only happen with attachments?
The documented issue is specific to sending an email with an attachment, so messages without attachments are not described as affected.
