This article applies to Exchange accounts which have 3rd-party mail filtering enabled with Barracuda, Reflexion, AppRiver etc.

Mail flow

When an outgoing message is sent from a domain that uses a third-party mail filtering solution for outbound messages, sometimes the message will fail the SPF check in the recipient's mail filter.

The reason for the failure is that the SPF record for the sender’s domain does not include information about the sender's 3rd-party outbound mail filtering solution. The SPF record informs the recipient mail filter which servers are authorized to send messages for the domain. If the sending server is not included in the SPF record, the message will fail authentication and can be dropped or sent to the recipient's Junk mail folder, depending on the configuration of the recipient's mail filter.

Read the Knowledge Base article on What Is An SPF Record? How Do I Change It? for more information how to create an SPF record.

The SPF record needs to be changed through the control panel of the company hosting your domain (i.e. GoDaddy, Network Solutions, Intermedia, etc.).