![outlook 2016 invalid certificate outlook 2016 invalid certificate](https://blog.rmilne.ca/wp-content/uploads/2015/06/image_316723D1.png)
![outlook 2016 invalid certificate outlook 2016 invalid certificate](https://support.content.office.net/en-us/media/342c14e7-0fc4-49ed-d179-df5f39afc7f2.png)
=> This change will take effect soon after the user closes & reopens the outlook, however the default autodiscover refresh internal is 1 hour, so it’s better to test after an hour or so. => Next run IIS reset or simply recycle the AutoDiscover AppPool in the IIS Manager. Set-OutlookAnywhere -Identity “EXCH201301Rpc (Default Web Site)” -InternalHostname -InternalClientsRequireSsl $true => To resolve this issue, we can run the following command to match the Internal Host name to the External host name as in the certificate SAN entry: => You will find that the internal host name is missing in the certificate. => Compare these two entries with the list of names we collected from the client machines certificate.
![outlook 2016 invalid certificate outlook 2016 invalid certificate](https://www.cert2brain.com/Server/quest/Quest_70-345_161_1.png)
=> Now go the Exchange Server, Launch Exchange Management Shell.’ Names listed in the certificate & make a note of them. => You will get a certificate error, click on the top red x mark next to the address bar. => Copy the URL for “ Only connect to the proxy servers that have this principle name in their certificate” & try to browse it. => Now click the Exchange Proxy Settings. => Select the email account and then click Change. => On the user’s machine launch Outlook=> Click File => Go to Outlook is unable to connect to the proxy server. The name on the security certificate is invalid or does not match the name of the target site “” There is a problem with the proxy server’s security certificate. Let’s take a look at an issue where users keep getting the following pop up in the outlook client frequently.