Hello @JillR031 ,
Can you please provide a screencap or the exact wording of the message? Is it occurring in your test sends or live sends? Is it occurring for everyone you send the email to, or just ones in your organization / using the same internal domain as you? Does applying authentication or making sure your email address / our domains are safelisted in your internal systems alleviate the issue? If there's a button for Looks Safe, does simply clicking that make your other test emails open without warning?