Summary
Internal emails can be flagged as impersonation despite SPF and DKIM verification due to a multitude of factors. Simple mail security setups may consider emails sent from a domain via a third-party provider to recipients within the same domain as impersonation. Restrictive internal policies and filters, especially in enterprise environments like Office 365, often override authentication protocols and flag emails based on sender patterns or aggressive anti-phishing measures. Issues during internal handoffs within email infrastructure, such as those involving Messagelabs/Microsoft, can disrupt authentication processes. Incorrect SPF, DKIM, and DMARC configurations, particularly overly strict DMARC policies (e.g., p=reject), can lead to the rejection of legitimate emails. Additionally, a low domain or IP reputation and issues related to email forwarding and multiple server hops can also invalidate authentication. If email authentication is new, the IP and domain will need to warm up.
Key findings
- Simple Mail Security Setups: Basic security configurations often flag emails sent from a domain via a third-party provider to recipients within the same domain as impersonation.
- Restrictive Internal Policies and Filters: Enterprise environments and internal email systems may have policies and filters that override authentication and flag emails based on sender patterns or aggressive anti-phishing measures.
- Internal Infrastructure Issues: Internal handoffs within email infrastructure (e.g., Messagelabs/Microsoft) can disrupt the authentication process.
- Incorrect SPF/DKIM/DMARC Configuration: Incorrect or overly strict SPF, DKIM, and DMARC policies, especially DMARC set to reject (p=reject), can cause legitimate emails to be rejected.
- Low Domain/IP Reputation: A poor domain or IP reputation can cause emails to be flagged as impersonation despite proper authentication.
- Email Forwarding Issues: Internal emails forwarded through external services may fail SPF checks if the forwarding server isn't authorized.
- Multiple Server Hops: Multiple server hops can invalidate SPF/DKIM results if servers modify email headers or content after authentication.
- Newly Authenticating Emails: When emails are newly authenticating with SPF and DKIM the email provider might not trust the domain as it does not have a reputation.
Key considerations
- Assess Security Setups: Evaluate whether basic security setups are overly restrictive and flagging legitimate emails as impersonation.
- Review Internal Policies and Filters: Examine internal email policies and filters to ensure they do not override authentication protocols and flag emails unnecessarily.
- Investigate Infrastructure: Investigate and address any issues related to internal handoffs within your email infrastructure that may be disrupting authentication.
- Adjust SPF/DKIM/DMARC Policies: Review and adjust SPF, DKIM, and DMARC policies to ensure they are correctly configured and not overly strict.
- Improve Domain/IP Reputation: Work to improve your domain and IP reputation through consistent sending practices and low complaint rates.
- Configure Email Forwarding: Properly configure email forwarding to ensure that forwarded emails pass SPF checks.
- Maintain Email Integrity: Ensure all servers in the email path maintain email integrity to prevent authentication invalidation.
- IP and Domain warm up: If you are newly authenticating, warm up your IP and domain reputation by sending a consistent volume of emails.
What email marketers say
11 marketer opinions
Internal emails may be flagged as impersonation even with SPF and DKIM verification for several reasons. Primarily, internal email systems or Microsoft 365 policies may have overly restrictive filters that flag emails from third-party providers as suspicious, especially if the provider isn't recognized as a legitimate sender. Incorrect SPF and DMARC configurations, such as DMARC policies set too strictly, can also cause emails to be rejected. A low domain or IP reputation can also trigger impersonation flags. Additionally, issues like email forwarding and multiple server hops can invalidate authentication. Starting authentication recently means reputation hasn't yet been established and can result in impersonation flags.
Key opinions
- Restrictive Internal Filters: Internal email systems might have filters that flag emails from third-party providers as impersonation due to security concerns.
- Incorrect DMARC Configuration: DMARC policies set to reject or quarantine emails can flag legitimate emails if they fail SPF or DKIM checks.
- Low Domain/IP Reputation: A poor domain or IP reputation can lead to emails being flagged as impersonation, even with proper authentication.
- SPF Forwarding Failures: Internal emails forwarded through external services may fail SPF checks if the forwarding server isn't authorized in the SPF record.
- Email Hop Issues: Multiple server hops can invalidate SPF/DKIM results if servers modify email headers or content after authentication.
Key considerations
- Review Internal Filters: Examine and adjust internal email policies and filtering rules to ensure they recognize and trust emails from your third-party provider.
- Correct DMARC Policy: Ensure your DMARC policy is correctly configured and aligned with your email sending practices to avoid unintended rejections.
- Improve Domain/IP Reputation: Consistently send high-quality emails and maintain low complaint rates to improve your domain/IP reputation.
- Configure Forwarding: Properly configure your email servers to handle forwarded emails to prevent SPF failures.
- Maintain Email Integrity: Ensure that all servers in the email path are configured to maintain the integrity of the email to prevent authentication invalidation.
- Email Authentication Reputation: If you have only just started authenticating emails, ensure you warm up your IP and domain reputation by sending a consistent volume of emails.
Marketer view
Email marketer from EmailGeeks forum responds that internal email systems may flag emails from third-party providers as impersonation if the internal system is configured to treat all emails that originate outside of the organization's network as suspicious. Review your internal email system's configurations and adjust the settings to trust emails coming from your authenticated third-party provider.
21 Jul 2024 - EmailGeeks forum
Marketer view
Marketer from Email Geeks shares that if you’ve just now started authenticating your mail with SPF and DKIM and DMARC, this is the first that Google has seen mail that’s associated with these newly authenticating identifiers. These newly authenticated identifiers have not yet established any kind of reputation at Google, but they will establish a reputation over time as more and more mail associated with those authenticated identifiers is sent to Google. Once those reputations are established, then the authentication will ensure that you get the deliverability you deserve.
4 Jan 2025 - Email Geeks
What the experts say
4 expert opinions
Internal emails can be flagged as impersonation even with SPF and DKIM due to several factors. Simple mail security setups often consider emails sent from a domain via a third-party provider to recipients within that same domain as impersonation. In addition, restrictive internal policies, particularly within enterprise environments, can override authentication protocols and flag emails based on sender patterns. Issues related to internal handoffs within email infrastructure like Messagelabs/Microsoft can also disrupt authentication. Furthermore, DMARC policies set too strictly (e.g., p=reject) can lead to the rejection of legitimate emails that fail authentication checks.
Key opinions
- Simple Mail Security: Basic security configurations often flag emails sent from a domain via a third-party provider to recipients within the same domain as impersonation.
- Restrictive Internal Policies: Enterprise environments and internal email systems may have policies that override authentication and flag emails based on sender patterns.
- Internal Infrastructure Issues: Internal handoffs within email infrastructure (e.g., Messagelabs/Microsoft) can disrupt the authentication process.
- Strict DMARC Policies: DMARC policies set too strictly (p=reject) can cause legitimate emails that fail authentication checks to be rejected.
Key considerations
- Assess Security Setups: Evaluate whether basic security setups are overly restrictive and flagging legitimate emails as impersonation.
- Review Internal Policies: Examine internal email policies to ensure they do not override authentication protocols and flag emails unnecessarily.
- Investigate Infrastructure: Investigate and address any issues related to internal handoffs within your email infrastructure that may be disrupting authentication.
- Adjust DMARC Policies: Review and adjust DMARC policies to ensure they are not overly strict and causing legitimate emails to be rejected.
Expert view
Expert from Email Geeks notes that the external authentication looks good, but there’s an internal handoff at messagelabs/Microsoft that’s breaking things, but is unsure how much of an issue that is.
3 Aug 2023 - Email Geeks
Expert view
Expert from SpamResource answers that emails from a 3rd party can be flagged even with SPF/DKIM, due to internal policies overriding authentication protocols. These policies identify emails as impersonation based on sender patterns, regardless of authentication. Review internal filters.
23 Jan 2023 - SpamResource
What the documentation says
3 technical articles
Even with SPF and DKIM verification, internal emails can be flagged as impersonation due to strict receiving mail server configurations or conflicting authentication settings within an organization, as highlighted by Microsoft Learn. Google Workspace Admin Help emphasizes that internal spoofing can arise from improper inbound mail authentication, necessitating correct setup of SPF, DKIM, and DMARC records, along with adjustments in the Google Admin console. DMARC.org adds that organizational policies not correctly configured for internal senders routed through external providers can lead to internal spoofing, underscoring the importance of properly configuring internal authentication.
Key findings
- Strict Server Configuration: Receiving mail servers may have overly strict configurations that flag internal emails even with proper SPF and DKIM.
- Conflicting Authentication: Conflicting email authentication settings within the organization's email environment can cause impersonation flags.
- Improper Inbound Auth: Internal spoofing arises from improper inbound mail authentication.
- Incorrect Organizational Policies: Organizational policies not correctly configured for internal senders routed via external providers can lead to spoofing.
Key considerations
- Review Server Settings: Examine receiving mail server configurations for overly strict settings that may be flagging legitimate internal emails.
- Resolve Authentication Conflicts: Identify and resolve any conflicting email authentication settings within the organization's email environment.
- Setup Authentication Records: Properly set up SPF, DKIM, and DMARC records to ensure proper authentication of inbound mail.
- Configure Policies: Correctly configure organizational policies to handle email from internal senders routed through external providers.
Technical article
Documentation from DMARC.org answers that internal spoofing can happen when organizational policies are not correctly configured to handle email from internal senders that are routed through external providers. It is important that your internal authentication configurations are correctly set up.
18 Oct 2022 - DMARC.org
Technical article
Documentation from Google Workspace Admin Help explains that internal spoofing can occur if inbound mail isn't properly authenticated. This documentation also explains how to make sure mail is authenticated, including setting up SPF, DKIM, and DMARC records, as well as adjusting settings for inbound mail in the Google Admin console to detect and manage spoofing attempts.
24 Apr 2025 - Google Workspace Admin Help
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