OWA “Manage Add-ins” Stuck Loading After Clicking Settings (Exchange 2019 CU15 / Exchange SE RTM)

I forced OWA/EWS to use the corporate proxy via system.net/defaultProxy because, in CU15/SE, the IIS/.NET HTTP/HTTPS calls were not honoring WinHTTP/InternetWebProxy. In a network with outbound traffic blocked, that was causing failures.

The bypasslist was adjusted to use valid regex patterns so we wouldn’t break OWA, keeping only internal exceptions.

I solved the problem doing those configurations:

# 1) Check current settings (on the current server)

Get-ExchangeServer $env:COMPUTERNAME | fl Name,InternetWebProxy,InternetWebProxyBypassList

# 2) Configure the proxy on Exchange (recommended)

Set-ExchangeServer $env:COMPUTERNAME -InternetWebProxy http://proxy.email.domainlocal.prv:3128

# 3) (Optional | I didn’t use it; it’s not necessary) Set the bypass list ONLY with valid FQDNs (no IP/localhost/[::1]/wildcards)

# Example: keep the server itself out of the proxy

Set-ExchangeServer $env:COMPUTERNAME -InternetWebProxyBypassList @("SRVMBX01.domainlocal.br")

# 4) Validate again

Get-ExchangeServer $env:COMPUTERNAME | fl Name,InternetWebProxy,InternetWebProxyBypassList

# 5) Apply to ALL Exchange servers (to avoid intermittent behavior behind the load balancer)

$proxy = http://proxy.email.domainlocal.prv:3128

Get-ExchangeServer | ForEach-Object {

if ($null -eq $_.InternetWebProxy -or [string]::IsNullOrWhiteSpace([string]$_.InternetWebProxy)) {

Write-Host "Setting proxy on: $($_.Name)" -ForegroundColor Cyan

Set-ExchangeServer $_.Name -InternetWebProxy $proxy

}

}

# 6) List any servers still missing a proxy (verification)

Get-ExchangeServer | Select Name,InternetWebProxy | Sort Name

# 7) Restart IIS on the server (run on each node serving OWA/ECP)

iisreset /restart

# 8) Rollback

#Set-ExchangeServer $env:COMPUTERNAME -InternetWebProxy $null -InternetWebProxyBypassList $null

#9 Set the proxyaddress

C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa

<defaultProxy>

<proxy proxyaddress=http://proxy.email.domainlocal.prv:3128 bypassonlocal="true" />

<bypasslist>

<add address="&lt;local&gt;" />

<add address="(^|\.)domainlocal\.net\.br$" />

<add address="^localhost$" />

<add address="^127\.0\.0\.1$" />

<add address="^\[::1\]$" />

</bypasslist>

</defaultProxy>

Or

<system.net>

<defaultProxy>

<proxy proxyaddress=http://proxy.email.domainlocal.prv:3128 bypassonlocal="true" />

<bypasslist>

<add address="&lt;local&gt;" />

<add address="(^|\.)domainlocal\.net\.br$" />

<add address="^localhost$" />

<add address="^127\.0\.0\.1$" />

<add address="^\[::1\]$" />

</bypasslist>

</defaultProxy>

</system.net>

<system.webServer>

<!-- allows the server to data stream immediately from client-->

# Recicle o AppPool do OWA
Import-Module WebAdministration
Restart-WebAppPool MSExchangeOwaAppPool

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It's working so far, no problem yet. Microsoft Professional Support has fallen behind so far; I’m ahead of them.

But, I have questions about EWS?

There is no proxy setting (or at least I couldn’t find one) in the files under the two EWS directories below. Can you confirm whether a proxy also needs to be configured somewhere else, and if so, where and what the correct syntax is?

Also, for the directories below, I didn’t see any proxy configuration either:

• C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\exchweb\ews

• C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Sync

• C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\ews

• C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa

• C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\sync

AND

These values to <bypasslist>is the right way? I'm using it.

<add address="&lt;local&gt;" />

<add address="(^|\.)domainlocal\.net\.br$" />

<add address="^localhost$" />

<add address="^127\.0\.0\.1$" />

<add address="^\[::1\]$" />

Other values occur this error:

X-ClientId: 150811E942E94E01A485410A98FFA61E

request-id 5a872104-4641-424b-98f6-9b6e016cf47f

X-OWA-Error System.Configuration.ConfigurationErrorsException

X-OWA-Version 15.2.2562.35

X-FEServer SRVMBX01

X-BEServer SRVMBX01

Date:10/02/2026 23:38:23

InnerException: System.ArgumentException