ATTN: Corporate Firewall Management Team/BlackBerry Enterprise Server Administrator
To ensure the best possible BlackBerry® experience we recommend ensuring your BlackBerry® Enterprise Server settings are up to date and follow our recommended configuration.
We have identified a possible configuration setting that may cause sporadic connectivity issues. If you use the US DNS of us.srp.blackberry.com and only allow certain IPs on your firewall, you may have already experienced or may experience intermittent connectivity issues. For more information, please refer to Ensure your BlackBerry Enterprise Server settings ... - BlackBerry Support Community Forums