Out: 220 ppp.full.hostname ESMTP Postfix (Ubuntu)
In: EHLO smtp.test.host
Out: 250-ppp.full.hostname
Out: 250-PIPELINING
Out: 250-SIZE 51200000
Out: 250-VRFY
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-AUTH CRAM-MD5 LOGIN PLAIN DIGEST-MD5
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In: MAIL FROM: SIZE=13675
Out: 250 2.1.0 Ok
In: RCPT TO: ORCPT=rfc822;mail@recipient.hostname
Out: 250 2.1.5 Ok
In: DATA
Out: 354 End data with .
Out: 451 4.3.0 Error: queue file write error
In: QUIT
Out: 221 2.0.0 Bye

è necessario disinstallare postfix e installare qmail, come consigliato sul forum della parallels:

http://kb.parallels.com/en/6394