What is causing the "on behalf of" text in the From header?
Some email clients, like Outlook and Gmail, will change the From: header of email messages sent from our Mailing Lists.
When the email is not sent from the normal server for that particular sender, the phrase "on behalf of" is added.
We keep the From: header of the original sender, which is recorded in the extended (hidden) header description. This is how your software knows the original sender's name to use after "on behalf of".
Your software is trying to provide insight into where the email actually came from. If you don't recognize either the name or email address, the email could be potentially fraudulent.
In the example below, your software found that "John Smith" is the original sender, but it was actually sent from the IP address for "[email protected]".
Basically, your software is altering the header to include the Mailing List address that actually sent the message. This is just to provide helpful details for you to know if the email is safe or not.