Upon setting up active sync with your windows mobile device and exchange server you may be greeted with this error message Security Certificate on the server is not valid. Error 0x80072F0D This is down to your device needing the certificate from the server to use Outlook Mobile Access. To download a self signed certificate on your site follow these instructions Go to your outlook webaccess address ( Usually mail.yourdomain.com/owa ) You might be greeted with a warning “There is a problems with this website’s security certificate” If so choose : “Continue to this website ( Not recommended )” You should also see this Click to view the certificate Click on Install Certificates, Click Next Check “Place all certificates in the following store” Choose one of the stores ( e.g. Personal ) Run through the rest of the screens Navigate to Start -> Run -> certmgr.msc Goto the store selected you saved the certificate to Right click on the certificate, select All Tasks -> Export Export this certificate to a .cer file somewhere on your computer Open Active sync and copy the .cer file from your computer onto the phone into a folder you will be able to access on the phone e.g. Business Using file explorer ( Located in Start , Programs ) on the Mobile Device , open the folder you saved the .cer certificate file you and open the .cer file itself It should ask you if you would like to install the certificate Install the certificate , and this should solve your syncing problem If you certificate has been provided from a trusted root provider , you may need to download their root certificates onto the phone as well e.g. Equifax Go Daddy