JVH Consulting's Blog

Client had issue where outlook refused to open because of the error below:

We can’t connect you.
Looks like we can’t connect to one our our services right now. Please try again later, or contact your helpdesk if the issue persists.
 
HTTP 404
login.microsoftonline.com

Office Outlook 365, Windows 10 machine. 

User could access their O365 mailbox via website (outlook.office365.com) but application would not open.

Found this reference site that explained what didn’t work: https://answers.microsoft.com/en-us/outlook_com/forum/all/fix-error-connecting-outlook-to-m365-http-404/bef8d6c5-a5c4-498b-ac72-bc81defb8256

I recalled I had something like this to force MFA for outlook, and just added two more items from above link to get outlook to open/work properly.

Windows Registry Editor Version 5.00
    
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001
    
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001
    
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001
    
[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319]
"SystemDefaultTlsVersions"=dword:00000001
"SchUseStrongCrypto"=dword:00000001

[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\AutoDiscover]
"ExcludeHttpsRootDomain"=dword:00000001
"PreferLocalXML"=dword:00000000
"ExcludeHttpRedirect"=dword:00000000
"ExcludeHttpsAutodiscoverDomain"=dword:00000001
"ExcludeScpLookup"=dword:00000001
"ExcludeSrvRecord"=dword:00000001
"ExcludeExplicitO365Endpoint"=dword:00000001

[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity]
"EnableADAL"=dword:00000001
"Version"=dword:00000001
"DisableADALatopWAMOverride"=dword:00000001
"DisableAADWAM"=dword:00000001

[HKEY_CURRENT_USER\Software\Microsoft\Exchange]
"AlwaysUseMSOAuthForAutoDiscover"=dword:00000001

Update: 2/10/2024 - Received another error while trying to Activate Office 365 on new PC. Error code 80090034 - Your computer's Trusted Platform Module has malfunctioned. This is similar to the other article with error 80090016 - where you open Device Manager and uninstall the TPM 2.0 and reboot. 
This didn't work for the 80090034. Instead had to add another registry item to the above registry file: 


[HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\Protect\Providers\df9d8cd0-1501-11d1-8c7a-00c04fc297eb]

"ProtectionPolicy"=dword:00000001



The section in bold made outlook work again but everything else is good to add as well when dealing with outlook, modern auth and autodiscover issues. 

Cheers!