MS365 Hosted Exchange Traffic on Outlook being blocked and redirected to Github.io and causing certificate errors

Support
1

Hi All

A bit of a noob here, when it comes to Nethserver. This system was setup by someone else quite a few years ago, and I have managed to familiarize myself with a few of the basics, but now I face a problem I have no idea how to solve.

I have been running this system for years with no issues, but suddenly, over the weekend, Microsoft Hosted Exchange email via Outlook, is no longer being passed through. I am able to set users up to connect via the web portal (outlook.office365.com) with no problem, but any time you try to access it via Outlook, it throws out a certificate error, and wont allow connections to the cloud server.

“The name on the security certificate is invalid or does not match the name of the site”

When checking to see who the certificate is issued by, it says Issued to: *.github.io, and Issued by: R12.

When checking the Squid Web Proxy logs, it shows me the below, almost like it is redirecting it to the github.io IP address

[Mon May 25 16:09:47 2026]     27 132.132.1.149 TAG_NONE/200 0 CONNECT 52.98.20.130:443 - HIER_NONE/- -
[Mon May 25 16:09:47 2026]     21 132.132.1.149 TCP_TUNNEL/200 3313 CONNECT outlook.office365.com:443 - HIER_DIRECT/185.199.110.153 -

When trying to open Lightsquid to troubleshoot, I keep on getting the below issue:

Service Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

I have tried restarting the service, as well as the Nethserver, all to no avail.

I would really appreciate any help anyone could offer as to where I can find what is causing this problem.

Cheers, Andrew

2

Hi @Watties74

This is probably because he hardcoded the domain in DNS.

M$ owns github so they can change the address.

Check your DNS resolutions and remove/change and it’ll all come backup after:

ipconfig/flushdns on Windows

Thanks,

1 Like
3

Thanks Jean Franco

We finally managed to get to the bottom of the issue. Although web filtering looked like it was enabled and working, it appears that ssl filtering had become corrupted. I eventually turned off filtering by process of elimination, and it started working again.

As said previously, this is a very old firewall, and it’s probably time to look at replacing it before it falls over.