People can make emails "appear" to be from whomever they want. As an example, try this site: http://emailpranker.com. See how you can send an email to yourself appearing to be from whomever you want? That's because the "From" line of the email header can contain whatever email address I want. However, if you look through the Message Headers, you can see exactly what server the email originated from. This is how many "phishers" (people trying to steal your passwords) work. They make their email appear to be from a legitimate source (such as gmail.com or whatever) and then either ask you to email back your account details or visit some phony website that looks like GMail. Do you understand now?
If not, I suggest taking a look at the PHP mail function.
The format for it is:
mail($SendTo, $SubjectofEmail, $BodyofEmail, $MessageHeaders);
By setting $MessageHeaders to "From: Heliohost_Account_Issues@gmail.com\r\n" the email will appear to be from the email address Heliohost_Account_Issues@gmail.com.
Coincidentally, that is almost exactly how Email Pranker sends out the "Prank" emails.