Outlook blocking addin request to localhost webserver

[mkondadg]

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Recently after Dec-10-2025 our Outlook addin is unable to communicate to localhost webserver.

Your Environment

• Platform : Windows 11 Pro 24H2
• Host : Outlook
• Office version number:

Microsoft Outlook Version: 1.2025.1218.100
Client Version: 20251212003.10
WebView2 Version: 143.0.3650.96 (Stable)

• Operating System: Windows

Expected behavior

Addin able to connect to localhost web server for GET/POST messages.

Current behavior

Addin unable to send HTTPS GET/POST messages

Steps to reproduce

It happens randomly when our addin connects to local HTTPS webserver.

NOTE :
When we start outlook using "olk.exe --devtools" to see network activity, addin connects successfully to local HTTPS webserver and later when outlook starts normally using olk.exe app, addin connects successfully.

Tested same thing using Chrome browser and needed "Local Network Access Checks" to be disabled for addin to communicate to local HTTPS webserver

Context

Unable to help data loss prevention from our addin.

[github-actions]

Here are some similar issues that might help you. Please check if they can solve your problem.

• Network Calls Blocked by WebView2 PNA Policy — No Way to Allow Local Network Access #6366
• Production Office Add-ins Cannot Connect to Desktop Applications in Chrome 142+ - Missing local-network-access Permissions Policy #6281
• Local add-in server resources blocked by CORS / Local Network Access in latest Chrome #6174

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Possible solution (Extracted from existing issue, might be incorrect; please verify carefully)

Solution 1:

Enable the LocalNetworkAccessRestrictionsTemporaryOptOut Edge policy and restart the affected machine.

Reference:

• Network Calls Blocked by WebView2 PNA Policy — No Way to Allow Local Network Access #6366 (comment)

Solution 2:

Modify the add-in iframe to include the allow="local-network-access" attribute. This allows the browser to prompt the user for Local Network Access permission, enabling the add-in to access localhost or private network resources.

Reference:

• Network Calls Blocked by WebView2 PNA Policy — No Way to Allow Local Network Access #6366 (comment)
• Production Office Add-ins Cannot Connect to Desktop Applications in Chrome 142+ - Missing local-network-access Permissions Policy #6281 (comment)

Solution 3:

Disable the 'Local Network Access Checks' flag in Chrome. This is a temporary workaround and not an ideal solution for production environments.

Reference:

• Local add-in server resources blocked by CORS / Local Network Access in latest Chrome #6174 (comment)

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[wenwolf]

It's still a problem for us as well and it hasn't been solved for the past 2 months now: allow="local-network-access" is still not there in the OWA add-on iframe...

Having the option to set this is a strong requirement for enterprises. It's not just a nice to have feature... See all the similar open requests already such as #6281, #6426, #6281, #6400, #6366...
Thanks

[rishi0107]

Hi @slabereemsft and @nbaliga18 — hope you are doing well🙏

We had a couple of quick questions to better understand the LNA behavior for Outlook add-ins:

1. Is there any expected timeline for fixing LNA-related issues in Outlook on the Web and New Outlook Desktop?

2. When this is addressed, will users see a browser-style LNA permission popup in Outlook Destop (New) , or will it handle this without showing a prompt?
   Will the behavior be the same in OWA and New Outlook Desktop?