When a phishing email is sent “on behalf of” someone, it means the message is impersonating or spoofing another individual or organization, often using manipulations in the sender field or email authentication.mailjet+2​

What “On Behalf Of” Means

• Email systems may display “on behalf of” or “via” when the sending server is not authorized for the domain in the “From” address, highlighting a potential mismatch and prompting suspicion about authenticity.mailgun+1​
• Attackers may exploit this mechanism by forging headers and making emails appear to be sent by trusted sources, such as company executives, distribution groups, or even the victim themselves, increasing the chances the user will interact with malicious content.reddit+1​

Impersonation and Spoofing Tactics

• Email Spoofing: Attackers forge the “From” address by manipulating email headers so the message appears to come from someone trusted, even though the underlying sender is fraudulent.proofpoint+1​
• Impersonation Attacks: Cybercriminals study targets and create emails that closely resemble the style, tone, and requests of legitimate senders, sometimes using similar domain names or display names to increase credibility.proofpoint+1​
• When organizations use third-party services to send emails, legitimate messages may also show “on behalf of” if authentication is incomplete, such as missing SPF or DKIM records.mailjet+1​
• In cases where a distribution group or corporate account is impersonated, external attackers may send emails “on behalf of” the group, even without actual delegation permissions.techcommunity.microsoft​

Red Flags for Recipients

• Seeing “on behalf of” or “via” alongside the sender name can be a warning sign, prompting users to verify the email’s authenticity, inspect headers, or check sending domain authorization.learn.microsoft+1​
• Always confirm sender information and avoid clicking on links or complying with urgent requests without verification, as these may be social engineering attempts linked to sophisticated phishing campaigns.bluevoyant+1​

This kind of technical impersonation is a staple tactic in phishing operations and should be treated as a risk indicator by both individuals and organizations.cloudflare+2​

 
1. https://documentation.mailjet.com/hc/en-us/articles/360042561834-Why-do-I-see-the-on-behalf-of-messages-in-my-emails
 
2. https://www.proofpoint.com/us/threat-reference/email-spoofing
 
3. https://www.proofpoint.com/us/threat-reference/impersonation-attack
 
4. https://help.mailgun.com/hc/en-us/articles/360012491394-Why-would-an-email-display-On-behalf-of
 
5. https://www.reddit.com/r/phishing/comments/1jevdr2/phishing_email_on_behalf_of_my_own_account_no/
 
6. https://techcommunity.microsoft.com/discussions/microsoft-365/phishing-email-sent-on-behalf-of-one-of-our-own-distribution-groups/2755549
 
7. https://www.cloudflare.com/learning/email-security/what-is-email-spoofing/
 
8. https://www.titanhq.com/security-awareness-training/phishing-email-impersonation/
 
9. https://learn.microsoft.com/en-us/answers/questions/4670652/on-behalf-of-emails-go-straight-to-junk
 
10. https://www.bluevoyant.com/knowledge-center/8-phishing-types-and-how-to-prevent-them

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