I entered an extra persona (email address) to my Zimbra account (Preferences)
The aim is to send out messages from the same account seemingly originating from different companies.

But in the Sent folder, I see both email addresses mentioned with "Send on behalf of"

primary email: glenn@primarycompany.com
persona: glenn@secondarycompany.com

sending mails with the persona yields this in the Sent folder

Sent by: glenn@primarycompany.com
On behalf of: glenn@secondarycompany.com

the mailbody text reads:
From: glenn@secondarycompany.com
Sender: glenn@primarycompany.com

What must I change for the Sent By/Sender Line not to appear in the mail?

best regards