To remove this alert from appearing please see the following article to add an SPF (Sender Policy Framework) entry to your DNS (Domain Name System) records - What is a SPF Record
Additionally, having an SPF record set up on your domain can help to prevent emails from being identified as SPAM.

Configuring DNS records are not supported by Blackbaud, as different providers have unique means in updating DNS records. Please contact the appropriate software vendor or IT professional for assistance with this process or issue, which is beyond Blackbaud's scope of support.