Yahoo! Groups may return email with a bounce message similar to the following:

We are unable to deliver the message from ________ to________@yahoogroups.com.

Your email was not delivered due to a suspected guidelines violation.

Yahoo! Groups now requires all incoming email to be authenticated by the sender’s email provider. This is a recent change which has greatly reduced the amount of spam posted to groups. Unfortunately, this change causes some legitimate emails to be blocked.

If you are using an external email application (Outlook, Thunderbird, Eudora, Incredimail, etc.), alternate webmail service, bulk-mailer, browser add-on, or scheduled email service to send email:

External email applications (such as Windows Live Mail, Microsoft Outlook, Mozilla Thunderbird, Eudora, Incredimail, etc.) configured with an incorrect or non-authenticated SMTP email serverExample: Using a yahoo.com email address in the “From” field with an ISP’s SMTP mail server will result in a delivery failure. This is because an ISP does not use Yahoo! Mail's email system to prove the sender owns the yahoo.com email address. may result in delivery failure. This may impact customers previously able to send email to Yahoo! Groups without issue. 

If you are using automatic forwarding to funnel messages through an email address to Yahoo! Groups:

Automatically forwarded or redirected messages may not be delivered to Yahoo! Groups.  In these cases, the sender’s “From” address is retained on the message, but the message passes through your account instead of being delivered by the sender’s SMTP server directly to Yahoo! Groups. Ask your senders to address these messages directly to your group’s official email address (______@yahoogroups.com, ______@egroups.com, etc.). If they are not a member of your group, feel free to invite them to join.

If you are receiving a delivery failure notice for a message you did not send:

If the failure notice is coming from a group you belong to, it’s possible your account was compromised.  In these situations, it’s always best to start by changing your email account password. If you use Yahoo! Mail, learn about managing your account when unsolicited email is sent to contacts from your account. For other email providers, please consult your provider’s support resources for further assistance.

It’s also possible your email address was spoofed, whether or not you may belong to a Yahoo! group. "Spoofing" is a tactic commonly used by spammers whereby they forge the email headers to make it appear as though the message came from a trusted individual. Unfortunately, there is no industry-wide technical solution to this problem, and Yahoo! Groups is not always able to prevent email spoofers from posing as group members. In the case of spoofing, the only solution is to delete the failure notice you received.

If none of the above solutions address or resolve this issue:

If you have the option and haven’t already done so, try re-sending the same exact message through the webmail service affiliated with your email address.  Webmail messages should always be properly authenticated and deliverable as long as they do not contain “spammy” content. If you receive the same delivery failure notification, our spam filters may have detected a “false-positive” message. Occasionally in our efforts to make Yahoo! Groups a more secure and spam-free service, we may incorrectly classify some mails as spam. We regret every such instance.

If you intended to send an email to Groups and received the delivery failure message due to a possible spam-filtering error, please contact our Customer Care team.