SSL Certificate Warning | Office 365 / Exchange Online & CloudFlare
Email warning popup relating to SSL and cannot verify the server identity message when using Outlook Apple Mail iPhone email

SSL Certificate Warning – Office 365 / Exchange Online and CloudFlare


Symptoms

  • Your device connects to your Office 365 / Exchange Online email account
  • The device pops up a security or SSL certificate warning complaining of:
    • an invalid name
    • “Cannot Verify Server Identity”
    • “A secure connection could not be established with the server”
    • or equivalent message
  • When you view the certificate details, you’re being issued an SSL certificate in the name of CloudFlare (cloudflare-dns.com)
  • You now scratch your head and wonder why CloudFlare is issuing certificates when you’re trying to talk to Microsoft Office 365

 

Cause and Remedy for SSL Certificate Warnings

CloudFlare is nothing to do with Office 365. So the question is, why does CloudFlare return a certificate when you were trying to communicate with Microsoft?

CloudFlare provide DNS services. Without technical detail, this is basically what makes the internet work, in the way most people understand and use it. DNS ensures that all your internet traffic reaches the correct destinations.

CloudFlare offers a service called DNS Proxying. In simple terms, it intercepts all requests to your domain (e.g your website). It then forwards them on to your web server if they look legitimate. So, any malicious attacks involving a denial-of-service for example (a big flood of traffic designed to stop your website from working) do NOT hit your website directly. They are hoovered up by CloudFlare and blocked.

If your nameservers are with CloudFlare (ask your IT people), you should log into CloudFlare and check to see if the autodiscover “A” record is being proxied. If so, CloudFlare is intercepting any requests by your device when it attempts to use this vital Microsoft autodiscover process, and passes it through to Microsoft. CloudFlare acts as a proxy.

This explains why you get a mismatch on the certificate and how CloudFlare is mysteriously getting in the way, even though we’re trying to talk to Microsoft. To be fair, it seems that most of the time it’s seamless and works fine anyway. But if you get repeated password prompts in Outlook or any kind of SSL certificate / security warning about an invalid certificate or mismatched name, this is likely to be the cause.

Since you don’t care if Microsoft receives a DoS attack, as it’s not your problem, it’s fine to turn off proxying for the autodiscover record on its own. This means that when your device attempts to retrieve email, it talks to the autodiscover service. But Cloudflare doesn’t intercept that request and hence you don’t get the SSL warning.

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Date Name Comments
Sep 22nd Alastair B Dean, sorted out the outstanding aspects of my e-mail verification update swiftly, courteously and competently - with a good sense of humour
Sep 22nd Pedro M Very quick response. Willing to sort the problem themselves via TeamViewer if needed there and then.
Sep 15th Simon K very good - great support
Sep 14th Sally & Made lots of sense - thank you
Sep 11th Yvonne C Thanks again for a super fast resolution Yvonne
Sep 9th Carl B James managed to find the issue which was partly an issue with the way the Macs were set up and also the way some of the Windows folders had been set up. The fix worked and I'm very pleased with how quickly everything was resolved.
Sep 4th Alastair B Swift and successful response - thank you for your help
Aug 28th Lynn H Very prompt support. Problem diagnosed and then fixed. Brilliant service. Many thanks
Aug 14th Lynn H Great Service. I am up and running again. Many Many thanks
Aug 6th Matt H Very quick resolution, thanks.