Last Updated: March 18, 2022
ISSUE
Outlook on Windows 7 and legacy Windows versions stop connecting to Microsoft 365 mailboxes.
STATUS: FIXED
After investigating the issue, most cases have been resolved by enabling TLS 1.2 on the Operating System per, Update to enable TLS 1.1 and TLS 1.2 as default secure protocols in WinHTTP in Windows Operating System updates mentioned on the article should be installed, and the following registry keys should exist:
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DefaultSecureProtocols registry entry:
Registry location for x86-based computers: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp DWORD name: DefaultSecureProtocols DWORD value: 0x00000A00
Registry location for x64-based computers: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp DWORD name: DefaultSecureProtocols DWORD value: 0x00000A00
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SecureProtocols registry entry:
Registry location: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings DWORD name: SecureProtocols DWORD value: 0x00000A80
Registry location: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings DWORD name: SecureProtocols DWORD value: 0x00000A80
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DisabledByDefault registry entry:
For TLS 1.1 Registry location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client DWORD name: DisabledByDefault DWORD value: 0
For TLS 1.2 Registry location: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client DWORD name: DisabledByDefault DWORD value: 0
TLS 1.2 should be enabled on all devices connecting to Microsoft 365 mailboxes. This is documented in the following article: Preparing for TLS 1.2 in Office 365 and Office 365 GCC - Microsoft 365 Compliance | Microsoft Docs Additionally, there were recent changes to the minimum required version of Office to connect to Microsoft 365 Mailboxes. This is kept and being constantly updated on this article: New minimum Outlook for Windows version requirements for Microsoft 365 - Microsoft Tech Community
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