How to remove the X_PRIORITY header

My emails are getting a negative spam score on my emails due to the X-Priority header that PHPlist inserts. Is there a way to remove the X-priority header? Thanks.

@NixPix The emails sent by my installation of phplist do not have that header, so I guess that it is being added by your outgoing mail server.

These appear to be the only X- headers added by phplist

X-Mailer: PHPMailer 5.2.14 (https://github.com/PHPMailer/PHPMailer)
X-phpList-version: 3.2.4
X-MessageID: 64
X-ListMember: xxxxx@yahoo.co.uk

The mail server seems to add a lot more

X-AntiAbuse:
X-Get-Message-Sender-Via: 
X-Authenticated-Sender: 
X-Source: 
X-Source-Args: 
X-Source-Dir:

Thanks for your response, Duncan. I’ll check with my ISP and see if they’re
adding it.