Up until recently I had all my company email accounts synced to my Windows Phone 8.1 device and PC's. We are using Outlook 2010 and Microsoft Exchange. A few days ago (last Monday to be exact) when I tried to sync my accounts I got the error message attached (error message is the same on both PC and phone).

Does anyone know what it means? Is it something our IT team has to look at? is there a problem with the SSL certificate file being used on Exchange? I tried adding and removing the accounts and it still gives the same error and I spoke to an IT staff member but they didn't know how to solve it.

I also tried manually adding the certificate file to my Windows Phone 8.1 device as .der, .crt and .p7c but each time my phone says this file cannot be opened.  I have not tried fixing it on my PC's.

My work PC, which connects directly to the same Exchange server via Outlook 2013, works fine.

How can I solve this?  Is it a certificate issue?  Is it a network issue (trying to access the Exchange server from outside the office)?. 

The OWA site works fine from the same PC's and phone with this error, except for displaying a message saying the certificate is not trusted, but I just bypass it and get to the login screen.

Many thanks.

• Edited by ianwuk 21 hours 15 minutes ago