Getting error VXNlcm5hbWU6

I'm getting an error that I presume is from postfix. The error is Error: authentication failed: VXNlcm5hbWU6
This error is generated from my website that is trying to send emails to members at registration. My website uses php mail. Would that be the reason and is there a way to edit postfix to allow my website to send mail.

look at the postfix log, perhaps it can shed some light

Code: [Select]

tail -f /var/log/maillog