The identity of the senders of e-mails passing through is
determined by a combination of the network address of the
SMTP peer that the message arrives from, and the envelope
return address.

Envelope return addresses alone are not sufficient to
validate an identity with any degree of certainty whatsoever,
as they are trivial to forge.  Adding the network address of
the SMTP peer into the equation makes forgery much more difficult.

Pay2send has applied for a patent on the concept of validating
sender identity with a combination of these two simple data.

Using universally available e-mail software, the pay2send system
allows only other people on the same network as yourself to
effectively forge your address.  Using properly configured universally
available e-mail software that authenticates the identites of
users and sets the envelope return addresses accordingly, the only
way to forge a sender address so that pay2send will improperly debit
your pay2send account is to defeat the authentication in use on
the system on your network.

If you did not understand the previous paragraph, set the "threshold"
in your pay2send account preferences to zero to eliminate the risk of
someone who uses the same outgoing e-mail server as you
using up your pay2send credit by forging e-mail from you.

A commercial e-mail sending operation should have adequate access
controls in place to prevent unauthorized messages from originating
in their equipment.