Send php mail with dedicated ip not with panel's address

[Xav2c]

Hi,

i'll try to make it simple and fast to read

panel address : domain[.]com
server hostname : srv01
server reverse : srv01.domain[.]com
server ip : ip.ip.ip.ip

customer domain on dedicated ip : customer[.]com
customer ip : ip2.ip2.ip2.ip2
customer ip reverse : customer[.]com

When a mail is sent using php.mail function (using wysija plugin in wordpress on customer[.]com website), the from header is :

Received: from srv01.domain[.]com (domain[.]com. [ip.ip.ip.ip])

How can i configure php to make it send mails from customer[.]com using ip2.ip2.ip2.ip2 address as if it was an independent server?

I am using plesk 11.5 and postfix

I tried adding these parameters in the domain interface in the additional parameters field:
sendmail_path = "/usr/sbin/sendmail -ffrom@customer[.]com -t -i"
sendmail_from = "contact@customer[.]com"

without luck

Any help appreciated