Email failure: "Suspected guidelines violation"
As a spam prevention measure, email messages sent to Yahoo Groups without SMTP-authentication often result in failed delivery, citing a “suspected guidelines violation.” This happens most frequently because you're attempting to send your message using an external email application (Microsoft Outlook, Mozilla Thunderbird, etc.). You can avoid errors by enabling SMTP-authentication within your email client or email service.
Enabling SMTP-authentication requires a different process for each email provider/service.
Sending from a Yahoo Mail address
Using an external email program
If you use an external email client, a browser add-on, or an alternate webmail, bulk mailer, or automated web service to send messages from your Yahoo Mail account, use our help article about setting up Yahoo Mail in an email program.
Using Yahoo Mail on the web
Don't want to go through the set-up process for an external email client? You can always use Yahoo Mail on the web to send messages to Yahoo Groups. All email sent via webmail are SMTP-authenticated by the Yahoo Mail servers.
Sending from a non-Yahoo Mail address
Since settings and configuration vary greatly for every email provider, please refer to your email provider's help or support website for assistance.
If you're having trouble sending your message using an external email client, you can also try sending your message using your email provider's webmail service (www.outlook.com, www.gmail.com, etc.). Messages sent from webmail should be properly authenticated and will be deliverable as long as they do not contain spam content.