Fixes / Outlook · Checked September 30, 2026

Outlook "Not implemented" error: what it means and how to fix it

Short answer

"Not implemented" in classic Outlook for Windows means Outlook asked a part of Office to do something (send, reply, create an event) and that part did not answer. The usual cause is a damaged Office install or a bad add-in. Start with Outlook.exe /safe. If the error goes away there, turn off your add-ins. If it doesn't, run an Online Repair of Office.

What this message means

The message is a generic Windows COM error (E_NOTIMPL). It means Outlook called a feature that did not respond the way it should. It does not mean your mailbox or the mail server is broken, because it happens inside Outlook on your PC before anything reaches the server. It mostly appears in classic Outlook for Windows (2013 to 2021 and Microsoft 365) when you press Send/Receive, Send, Reply All or Forward, or when you create or accept a calendar event. The usual causes are damaged Office registration after an update or a partial reinstall, an add-in that hooks into sending mail, a corrupt Send/Receive settings file, or 32-bit Office running on an ARM-based Windows PC.

Common causes

Cause	How to tell
A faulty or outdated add-in (antivirus mail scanner, CRM, PDF, meeting or archiving add-in) hooks into sending mail	The error goes away when you start Outlook with Outlook.exe /safe, and comes back in normal mode.
Damaged Office installation or registration, often after an Office or Windows update or when two Office versions are installed side by side	The error still appears in safe mode. Other Office problems often show up at the same time (Word or Excel files won't open, repair or uninstall fails). Settings > Apps may list two Office entries.
Missing write permission on the Office SecurityManager registry key (seen with Office 2019/2021 Click-to-Run, and it can come back after monthly updates)	You can receive mail but not send it, new calendar events also give "Not implemented", several PCs are affected, and the problem returns about once a month.
Corrupt Send/Receive settings file (.srs)	The error appears only when you click Send/Receive or when automatic Send/Receive runs. Replying and composing work normally.
32-bit Office running on a Windows PC with an ARM processor (for example Snapdragon Copilot+ PCs or Surface Pro X)	The error appears when you click Reply All or accept a meeting invite. Settings > System > About shows an ARM-based processor, and File > Office Account > About Outlook shows 32-bit.
Damaged Outlook profile	Everything above checks out, but a second profile with the same account works without the error.

How to fix it

1. Start Outlook in safe mode and find the bad add-in

Classic Outlook for Windows (Windows 10 and 11)

Close Outlook completely.
Press Windows key + R, type Outlook.exe /safe and select OK. Choose your profile if asked.
Try the action that failed (Send/Receive, Send, Reply All). If it works, an add-in is the cause.
Restart Outlook normally, then go to File > Options > Add-ins. Next to Manage: COM Add-ins, select Go.
Clear all the check boxes and select OK. Restart Outlook.
Turn the add-ins back on one at a time, restarting Outlook each time, until the error comes back. Then remove or update that add-in.

2. Reset the Send/Receive settings file

Classic Outlook for Windows

Close Outlook.
Press Windows key + R, type %appdata%\Microsoft\Outlook and press Enter.
Find the file whose name ends in .srs (usually Outlook.srs, or <your profile name>.srs).
Rename it to Outlook.srs.old (or move it to your desktop) rather than deleting it.
Start Outlook. It creates a new .srs file with default settings. Any custom Send/Receive groups need to be set up again.

3. Repair Office (Online Repair)

Windows 11: Settings > Apps > Installed apps. Windows 10: Settings > Apps > Apps & features.

Close all Office apps.
Windows 11: open Settings > Apps > Installed apps, find Microsoft 365 or Microsoft Office, select the three dots (...) and choose Modify. Windows 10: open Settings > Apps > Apps & features, select the Office entry and choose Modify.
Choose Quick Repair and select Repair. Test Outlook.
If the error comes back, repeat and choose Online Repair (it downloads Office again and takes longer).
If two Office versions are listed, uninstall the one you don't use first, then repair the other one.
Restart the PC and test again.

4. Give Users write access to the SecurityManager registry key

Office 2019 / 2021 Click-to-Run on Windows 10 and 11. Needs administrator rights. For IT admins or advanced users.

Close all Office apps. Press Windows key + R, type regedit and run it as administrator.
Back up first: File > Export, and save a copy of the registry.
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\REGISTRY\MACHINE\Software\Microsoft\SecurityManager.
Right-click SecurityManager, choose Permissions, and select the Users group.
Tick Allow for Full Control (or at least make sure Write is allowed), select Apply, then OK.
Close Registry Editor and start Outlook. If the problem returns after the next monthly update, check this permission again.

5. Create a new Outlook profile

Classic Outlook for Windows

Close Outlook.
Open Control Panel and select Mail (Microsoft Outlook). You can also go to File > Account Settings > Manage Profiles in Outlook.
Select Show Profiles, then Add, and enter a profile name.
Add your email account in the new profile.
Select Prompt for a profile to be used, select OK, then open Outlook and choose the new profile.
If the error is gone, set the new profile as the default under Always use this profile.

6. Switch to 64-bit Office on an ARM PC

Windows 11 on ARM devices running 32-bit Office

Check your Office version: in Outlook, go to File > Office Account > About Outlook and look for 32-bit or 64-bit.
If it says 32-bit, uninstall Office from Settings > Apps > Installed apps.
Sign in at account.microsoft.com (or office.com) and go to the install page.
Install the 64-bit version of Microsoft 365 or Office, then sign back in to Outlook.

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Still not fixed?

If none of these steps work, use Microsoft's Get Help app (search "Get Help" from the Start menu) to fully remove Office. Then delete the leftover Office folders under Program Files and AppData, restart, and reinstall. This removes local Outlook settings, so first export any PST data you store only on this PC. As a stopgap, send mail from Outlook on the web (outlook.office.com or outlook.com), which does not use your local Office install. On a work PC, contact IT and tell them "Not implemented" appears on Send/Receive and in safe mode. Mention the SecurityManager registry key, because a Group Policy or update may be resetting it on several machines.

Questions people ask

Does "Not implemented" mean my emails are lost?

No. The error happens inside Outlook on your PC, so your mailbox on the server is untouched. Messages you tried to send usually stay in the Outbox or Drafts until the problem is fixed.

Why does the error only appear when I click Reply All or accept a meeting?

Microsoft has documented this pattern on Windows PCs with ARM processors running 32-bit Office. Installing 64-bit Office fixes it. On other PCs the same symptom usually comes from an add-in that hooks into replies or meetings.

Why does the error keep coming back every month?

On Office 2019 and 2021, monthly updates can reset the permissions on the SecurityManager registry key. Check the Users write permission on that key again after updates, or have IT enforce it with Group Policy.

Does this happen in the new Outlook or Outlook for Mac?

The reports are almost all from classic Outlook for Windows, because the error comes from Windows COM components. The new Outlook for Windows and Outlook for Mac do not use these components, so switching to one of them is a workaround.

Can I just reinstall Outlook?

Outlook is part of Office, so run Office's Quick Repair or Online Repair first. A full uninstall and reinstall also works, but it takes longer and removes local settings.

Sources

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