We help IT Professionals succeed at work.
Get Started

Getting (Proxy server's security certificate) errors 18 and 10

Last Modified: 2015-10-12
Hello experts,

We have installed a new Exchange 2013 on a new Win 2012 server. The older exchange is 2010 on a Win 2008R2 server.

We plan to uninstall old Exchange 2010 later, right now we have all mailboxes migrated to the new exchange.

Now both mobile app access and owa are working well. We have the issue only with desktop Outlook. For few users only it's working well, for almost 90% of users they are receiving the famous message:

There is a problem with the proxy server's security certificate. The security certificate is not from a trusted certifying authority. Outlook is unable to connect to the proxy server mail.ourdomain.com. (Error code 18).

BTW, we don't have any signed certificate, but only using self-signed ones which are setup automatically upon installation of Exchange.

Any help solving this?
Watch Question
Transport Ninja
This problem has been solved!
Unlock 1 Answer and 4 Comments.
See Answer
Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

  • Troubleshooting
  • Research
  • Professional Opinions
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE