Summary
The 'Messages can be spoofed' warning in Outlook arises from a multitude of factors, encompassing both technical configurations and organizational policies. These include email security tools (e.g., Proofpoint), incorrect SPF/DKIM/DMARC records, internal security policies, shared hosting environments, or even incorrect system time. The warning can also be a false positive, remediable by whitelisting. Furthermore, the use of free email service providers for 'from' addresses or sender addresses similar to internal contacts may trigger the warning. Internally, stricter security measures by the receiving organization may also cause this warning, irrespective of external authentication.
Key findings
- Security Software: Email security tools can flag emails, even internal ones, as spoofed due to strict filtering rules.
- Authentication Problems: Improperly configured or missing SPF, DKIM, and DMARC records are a frequent cause.
- Internal Security Policies: Receiving organizations' internal email policies may trigger the warning.
- Shared Hosting Risks: Shared hosting can lead to warnings if another domain on the same IP is flagged for spam.
- False Positives: The warning isn't always accurate; whitelisting can resolve these instances.
- Free Email Issues: Using a free email domain as the 'from' address increases the likelihood of triggering the warning.
- Time Synchronization: Incorrect system time on the recipient's computer can interfere with authentication.
- Internal Settings: Internal security measures by the recipient organization can trigger the warning.
- Address Similarity: Sender addresses similar to internal contacts are also often flagged
- Reputation: Poor sender reputation or being on blocklists can cause the warning.
Key considerations
- Verify Authentication: Ensure SPF, DKIM, and DMARC are correctly set up for your domain.
- Contact IT Support: If problems persist, contact the recipient's IT department to investigate their security settings.
- Whitelist Senders: Consider whitelisting trusted senders to prevent false positives.
- Dedicated IP Address: If using shared hosting, consider a dedicated IP address to isolate your reputation.
- Monitor Blocklists: Check your domain's presence on email blocklists and address any issues.
- Use Custom Domains: Avoid using free email domains for business correspondence; use a custom domain instead.
- Time Accuracy: Ensure the recipient's system time is accurate.
- Review Security Logs: If using email security tools, check their logs to determine why messages are being flagged.
- Sender reputation: If the email is being sent from a marketing platform you should check that the reputation is good
What email marketers say
9 marketer opinions
The 'Messages can be spoofed' warning in Outlook can arise from various factors, including email security tools like Proofpoint, misconfigured SPF/DKIM/DMARC records, internal email security policies, shared hosting environments, or even incorrect system time settings. It can also be a false positive, and whitelisting the sender might resolve the issue. Using free email service provider for 'from' address may also trigger the warning.
Key opinions
- Security Tools: Email security tools such as Proofpoint may flag internal emails as spoofed due to strict filtering rules.
- Authentication Issues: Incorrect or missing SPF, DKIM, and DMARC records can cause Outlook to flag emails as potentially spoofed.
- Internal Policies: Internal email security policies within the recipient's organization might trigger the warning.
- Shared Hosting: Senders on shared hosting environments can be affected if another domain on the same IP address is flagged for spam.
- False Positives: The warning can sometimes be a false positive, requiring whitelisting of the sender.
- Free Email Domain: Using a free email domain in the 'from' address can cause outlook to show 'Messages can be spoofed' warning.
- Incorrect Time Setting: Having incorrect time and date setting on the computer can trigger this message.
Key considerations
- Check Authentication: Verify that SPF, DKIM, and DMARC records are correctly configured for the sending domain.
- Contact IT: If the issue persists, contact the recipient's IT department to inquire about internal email security settings.
- Whitelist Sender: If the sender is trusted, consider whitelisting their email address or domain to prevent false positives.
- Dedicated IP: If using shared hosting, consider switching to a dedicated IP address to avoid reputation issues.
- Sender reputation: If the email is being sent from a marketing platform you should check that the reputation is good
- Custom Domain: Consider to configure a custom domain instead of using a free email service provider domain.
- Time and Date: Check and sync the time and date setting on the computer.
Marketer view
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.
26 Feb 2024 - SuperUser
Marketer view
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.
23 Dec 2022 - StackExchange
What the experts say
2 expert opinions
The 'Messages can be spoofed' warning in Outlook, when appearing on internal emails, often indicates an internal security setting or stricter measures implemented by the recipient's organization. This is unrelated to external authentication protocols and is not visible to external parties.
Key opinions
- Internal Security: The warning typically stems from internal security settings within the recipient's organization.
- No External Impact: This warning is specific to the internal network and does not reflect authentication issues visible outside the organization.
- Authentication Irrelevant: The warning is not related to external email authentication methods (SPF, DKIM, DMARC).
Key considerations
- Check Internal Policies: Contact the recipient's IT department to understand the specific internal security policies in place.
- Ignore if Internal: If the warning only appears on internal emails, it might not require changes to external authentication configurations.
- Awareness: Be aware that such internal warnings are part of the organization's efforts to protect against phishing and spoofing attempts, even within their own network.
Expert view
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.
1 Jun 2022 - Word to the Wise
Expert view
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.
3 Aug 2021 - Email Geeks
What the documentation says
6 technical articles
The 'Messages can be spoofed' warning in Outlook is a security feature designed to alert users to potential phishing attempts and malicious emails. It's triggered by various factors, including sender address similarity to internal contacts, failure of authentication checks (SPF, DKIM, DMARC), DMARC policies set to 'quarantine' or 'reject', and listing on blocklists like Spamhaus. Email security appliances like Proofpoint also flag suspicious emails.
Key findings
- Anti-Phishing Measure: The warning is part of Outlook's anti-phishing measures to protect users from potentially malicious emails.
- Authentication Failure: Failure to pass authentication checks (SPF, DKIM, DMARC) can trigger the warning.
- DMARC Policies: DMARC policies set to 'quarantine' or 'reject' cause recipient servers to flag emails failing DMARC authentication.
- Blocklist Inclusion: Being listed on blocklists like Spamhaus can trigger the warning.
- Security Appliance Detection: Email security appliances (e.g., Proofpoint) detect suspicious characteristics and flag potentially spoofed messages.
- Similar sender address: Sender addresses similar to internal contacts are also often flagged
Key considerations
- Check Authentication: Ensure that SPF, DKIM, and DMARC records are properly configured to authenticate your emails.
- Review Logs: Review email security appliance logs to understand why messages are being flagged.
- Monitor Reputation: Monitor your sender reputation and ensure you're not listed on any blocklists.
- Address Similarity: Avoid using sender addresses that are similar to those of internal contacts within the recipient's organization.
Technical article
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.
16 Jun 2025 - RFC Standards
Technical article
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.
11 Feb 2024 - Proofpoint Support
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