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REAL FIX for Outlook 365 sign-in error 2604 is TLS 1.2

So there's a few threads on Microsoft forums giving ideas for overcoming error 2603 & 2604 sign in errors and they all miss the reason and leave us all frustrated!
When any of the Office 365 apps fail to allow sign-out and sign back in with either just a blank white popup window showing nothing OR with a basic "Failed to Sign In error" loop, it is 99% caused by your Internet Properties settings on your device not having a simple check mark against the "Use TLS 1.2" option.

For Windows systems: navigate to Internet Options in the Control Panel. In the Advanced tab, enable the ‘Use TLS 1.2’ option.

[I tried to upload a graphic for you in both .JPG and PNG, but no surprise, both times, the image uploader failed].
In other device systems, you need to find general Internet Options and look for supporting TLS at least version 1.2

ps. It would be nice for a forum Admin to pin this post to the other locked threads so that customers can at least find a proper answer to this widespread problem.

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Once you restart Outlook (all Office APPs) after applying the TLS setting, the error will disappear.

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In order to resolve Microsoft Teams error 2604, it is recommended that you reset your Internet properties as the issue is often related to the compatibility of the TLS version. The TLS versions that may be causing the problem include 1.0, 1.1, and 1.2. To do this, simply click on "Restore advanced settings" to reset them to their default configuration. Additionally, ensure that any active VPNs on your PC are disabled. This should help to address the error and improve the performance of Microsoft Teams.

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Didn't fix it for me.

My issue was not TLS 1.2. Turned out to be a bug in my virus protection software. Try turning off your firewall at the windows and/or anti-virus protection level AND your routers protection level, plus ensure TLS 1.2 is ticked and you might find it now works. (not a permanent fix though). Once I upgraded my anti-virus protection software, it's been working since (with my firewall re-enabled). You might also need to allow teams.exe into the 'trusted' list.

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Thank you so much!

I was searching around for over an hour with nothing but the usual "check your proxy / dns / network connection" recommendations which were all nonsense in my case.

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can't work into word apps

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Last updated March 14, 2025 Views 12,052 Applies to: