Gmail may sometimes display a red warning banner when you receive an email from suspicious senders, this has been commonly faced by many however below are the few ways by which you can declutter the email.
>Kindly reduce the number of links and images in the emails.
>Please make sure there’s an unsubscribe option in the emails. (Note: Test emails would not have them however original emails will definitely have a unsubscribe link).
>Check the email content and avoid spammy words.
>Make sure the email body and the subject line are relevant to the recipients.
>Disable any antivirus email signature.
>Scan your emails and always try to send the email to intended recipients.
In addition to the above always click on the "Looks safe" icon below the message if the email lands in the spam or junk folder so that you are making the email intended to you and Gmail learns from the user's behavior and past experiences.