Why am I seeing a 'Messages can be spoofed' warning in Outlook?
Summary
What email marketers say9Marketer opinions
Email marketer from SuperUser explains that the 'Messages can be spoofed' warning can appear if the sender is using a shared hosting environment where multiple domains share the same IP address. If one domain is flagged for spam, others on the same IP can be affected.
Email marketer from StackExchange indicates that the warning can sometimes be a false positive. They suggest the recipient whitelist the sender's email address or domain to prevent the warning from appearing.
Email marketer from Microsoft Community indicates that having incorrect time and date setting on the computer can trigger this message. As the authentication is time sensitive it causes issues. Set it to auto-sync and restart Outlook.
Marketer from Email Geeks shares that the client might have Proofpoint or a similar tool, which can cause this warning even for emails from their own domain.
Email marketer from MailChimp Resource responds that the 'Messages can be spoofed' warning may be shown when the 'from' address uses a free email service provider, like Gmail or Yahoo, on behalf of your domain. They suggest to configure a custom email domain instead.
Email marketer from Reddit user jsmith shares that the warning often appears when the sending server doesn't have proper SPF and DKIM records set up. They suggest checking the sender's DNS records to ensure they are correctly configured for email authentication.
Marketer from Email Geeks suggests that additional rules for incoming email warnings might be applied, or the DMARC policy is set to None.
Marketer from Email Geeks explains that the standard Spoof Intelligence detection might be turned on, indicating something missing from an authentication standpoint. Recommends the client's IT admin be consulted.
Email marketer from Email Marketing Forum user EmailGuru responds that the warning can be triggered by internal email security policies that are set up to detect potentially fraudulent senders. They recommend contacting the recipient's IT department to inquire about internal security settings.
What the experts say2Expert opinions
Expert from Word to the Wise explains that internal spoofing warnings often occur when a company has implemented stricter internal security measures. It is unrelated to external authentication and isn't seen by anyone outside the organization.
Expert from Email Geeks mentions that if the mail is coming into their domain, it's often an internal security setting, unrelated to authentication, and not visible outside the domain.
What the documentation says6Technical articles
Documentation from RFC Standards details that the email 'Messages can be spoofed' warning is a security feature implemented by email clients to alert users to potential phishing attempts. It explains how SPF, DKIM, and DMARC records are used to verify the authenticity of email senders and reduce spoofing.
Documentation from Proofpoint Support details that their email security appliance flags messages as potentially spoofed if they fail authentication checks or exhibit suspicious characteristics. They advise reviewing Proofpoint's logs to understand why the message triggered the warning.
Documentation from Google Workspace Admin Help states that similar warnings can appear if the sender's domain has a DMARC policy set to 'quarantine' or 'reject,' and the message fails DMARC authentication. They recommend checking the DMARC record of the sending domain.
Documentation from Microsoft Learn explains that the 'Messages can be spoofed' warning in Outlook indicates that the sender's email address is similar to someone in the recipient's organization or a frequently contacted domain. This is part of Outlook's anti-phishing measures to alert users to potentially malicious emails.
Documentation from Spamhaus shares that some mail servers use Spamhaus blocklists and other reputation databases to identify and flag potentially malicious emails. Senders listed on these blocklists may trigger spoofing warnings.
Documentation from Agari by Proofpoint notes that organizations use DMARC policies to instruct recipient mail servers on how to handle emails that fail authentication checks. A policy of 'reject' will cause those emails to be rejected and marked as potential spoofs, triggering the warning.