Last night (Feb 25th, 2013) around 5pm Central time Microsoft’s Forefront service FPE changed its security policies and began blocking most Mailive! test messages.
In the Forefront control panel it will be necessary to whitelist the sender mailive@knowledgefront.com or the IP Range where the test messages originate: 71.5.105.193 - 71.5.105.198 (netblock 71.5.105.192/29 or 71.5.105.192/255.255.255.248).
If there are any questions or problems feel free to contact us and we will help out any way we can.