Outlook 2013 Proxy error

Question

Hello,
We have recently deployed some Microsoft Surface Pro 3's in my office.  All of them have Office 2013 Basic and work when in the office.  However, a user is getting an error message on one of them when he uses the Surface Pro while traveling. 
The errror message is:  "There is a problem with the Proxy servers security certificate.  The certificate is not from a trusted certifying authority.  Outlook is not able to connect to the proxy server <server.companyname.com>.
(Error Code 8). 
I have Googled and BING'd this all morning and am not making much progress.  Items I have verified. 
Date and time are correct on the device
User does NOT get this error when he is INSIDE the office.
After acknowledging the proxy error, the user receives two security alerts, stating there is a problem with the sites security certificate. 
We have a valid certificate from GoDaddy on my Exchange 2010 server. 
None of my Windows 7 users are receiving this error. 
Thank you in advance for your time. 

Answer 1

Hinte
Below are the results you requests.  Thank you. 
[PS] D:\temp>Get-OutlookProvider
Name                          Server                       
CertPrincipalName             TTL
EXCH                                                                                                
    1
EXPR                                                                                                    
1
WEB                                                                                                      1
Try running:
Set-OutlookProvider Exch msstd:<subjectnameofcert>
Set-OutlookProvider EXPR msstd:<subjectnameofcert>
I have seen issues where Outlook doesn't like this not being populated. 
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