hola amigos tengo un server mail, squirrelmail+sendmail+mailscanner y empieza a aparacer mensajes asi... tengo en un lapso de 25 minutos estos:

The original message was received at Fri, 4 Jan 2013 15:25:04 -0300
from localhost.localdomain [127.0.0.1]

----- The following addresses had permanent fatal errors -----

(reason: 550-5.1.1 The email account that you tried to reach does not exist.
Please try)

----- Transcript of session follows -----
... while talking to gmail-smtp-in.l.google.com.:
>>> DATA
<<< 550-5.1.1 The email account that you tried to reach does not exist. Please try
<<< 550-5.1.1 double-checking the recipient's email address for typos or
<<< 550-5.1.1 unnecessary spaces. Learn more at
<<< 550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596
d27si23792305anp.157
550 5.1.1 ... User unknown
<<< 503 5.5.1 RCPT first. d27si23792305anp.157

entiendo que puede ser porque la direccion del receptor no exista o sea erronea, o podria ser otra cosa?
Saludos
Gracias