This article applies to Exchange accounts which have 3rd-party mail filtering enabled(postini, mxlogic etc.).
By design of mail flow that includes 3rd-party mail filter solution, messages sent from domains, which do have SPF record, fail to pass Intermedia spam check. The reason of that failure is that SPF for sender’s domain does not include information about 3rd-party mail filtering solution.
Even though messages fail to pass spam check, they are not necessarily get deleted, they might appear in Junk folder (depending on you Advanced Email Security preferences). You might need to disable Intermedia spam filtering to be able to receive messages from domains with SPF record in your Inbox, to do so please login to OWA https://exchange.intermedia.net/ControlPanel/Login?ClientType=WebMail and navigate to Options > See All Options > Block or Allow and select Don't move e-mail to my Junk E-Mail folder.