email sent out reveals my Server ID

[baijianpeng]

I tried to use the SMTP server created by VestaCP to send test email to my Gmail account. Then I choose to "show original email" in Gmail, I found my Server ID inside those original information:

Received: from iM847i3uk6bA ([120.27.137.71])

This is dangerous. My VPS provider had told me to NOT tell other people what is my Server ID (the string iM847i3uk6bA ). But now my emails become a big leak!

What configuration file should I edit to change that information?

Thank you.