Bad sender address syntax ..

[Amedeo Rinaldo]

Weird 'Bad sender address syntax', where '""@' come from ? some ideas?
(see info below)

--
.''`. *Amedeo Rinaldo*
: :' : debian addicted ;-)
`. `'
`-

-------------------


OS: Debian squeeze (2.6.32-5-amd64)
Amavis: debian 2.7.0-1~bpo60+1 (amavisd-new-2.7.0 '20110701')
Postfix: debian 2.9.1-2~bpo60+1

(real data masked)

## mailq

-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
4082940175 4252 Wed Jul 11 09:16:46 ""@externaldomain.tld
(host 127.0.0.1[127.0.0.1] said: 451 4.5.0 Error in processing,
id=01823-04, quar+notif FAILED: Can't quarantine: 501 5.1.7 from
MTA(smtp:[127.0.0.1]:10025): 501 5.1.7 Bad sender address syntax at
/usr/sbin/amavisd-new line 14443. (in reply to end of DATA command))
reci...@mydomain.tld
-- 4 Kbytes in 1 Request.


## mail.log snip
..
Jul 11 09:16:46 mx20 postfwd2/policy[8975]: [RULES] rule=3, id=WL_003,
client=smtp.externaldomain.tld[111.222.333.444],
sender=<@externaldomain.tld>, recipient=<reci...@mydomain.tld>,
helo=<smtp.externaldomain.tld>, proto=ESMTP, state=RCPT, delay=0.00s,
hits=WL_003, action=DUNNO
Jul 11 09:16:46 mx20 postfix/qmgr[4250]: 4082940175:
from=<@externaldomain.tld>, size=4252, nrcpt=1 (queue active)
Jul 11 09:16:47 mx20 re-injection/smtpd[11314]: warning: Illegal address
syntax from localhost[127.0.0.1] in MAIL command: <""@externaldomain.tld>
Jul 11 09:16:47 mx20 amavis[11835]: (11835-17) (!)SEND from
<""@externaldomain.tld> -> <quara...@localsystem.tld>,BODY=7BIT 501
5.1.7 from MTA(smtp:[127.0.0.1]:10025): 501 5.1.7 Bad sender address syntax
Jul 11 09:26:29 mx20 postfix/qmgr[4250]: 4082940175:
from=<@externaldomain.tld>, size=4252, nrcpt=1 (queue active)
Jul 11 09:26:30 mx20 re-injection/smtpd[11722]: warning: Illegal address
syntax from localhost[127.0.0.1] in MAIL command: <""@externaldomain.tld>
Jul 11 09:26:30 mx20 amavis[12339]: (12339-14) (!)SEND from
<""@externaldomain.tld> -> <quara...@localsystem.tld>,BODY=7BIT 501
5.1.7 from MTA(smtp:[127.0.0.1]:10025): 501 5.1.7 Bad sender address syntax

[baj...@gmail.com]

Il 12/07/2012 18:13, Amedeo Rinaldo ha scritto:
>..[CUT]..
> ## mail.log snip
> ..

> Jul 11 09:16:46 mx20 postfix/qmgr[4250]: 4082940175: from=<@externaldomain.tld>, size=4252, nrcpt=1 (queue active)

> ..


Ok.. I've investigated a little and it come out that my postfix is
accepting email addresses with an empty local-part.
The postfix 'strict_rfc821_envelopes' configuration parameter handles
also this behaviour.. (default: disabled).
Amavis don't love it too much ( ""@domain.tld ) and "gracefully" stuck
.. with a probable DoS risk.

So, my fault.. I wasn't aware of this requirement
(strict_rfc821_envelopes=yes).

Ciao

[Mark Martinec]

Amedeo,

> Weird 'Bad sender address syntax', where '""@' come from ? some
> ideas? (see info below)

> Ok.. I've investigated a little and it come out that my postfix is
> accepting email addresses with an empty local-part.
> The postfix 'strict_rfc821_envelopes' configuration parameter handles
> also this behaviour.. (default: disabled).
> Amavis don't love it too much ( ""@domain.tld ) and "gracefully" stuck
> .. with a probable DoS risk.
>
> So, my fault.. I wasn't aware of this requirement
> (strict_rfc821_envelopes=yes).

It's a case of 'garbage-in/garbage-out'. Neither a null local part
nor a "" are valid, but Postfix chose to mercifully permit the
first but not the second, unless strict_rfc821_envelopes=yes.

RFC 5322 requires quoting of a local part which is not following
a dot-atom syntax, which is what amavisd did, at least until
version 2.4.0:


amavisd-new-2.4.0 release notes

- no longer bother to convert addresses like <""@yahoo.com> to <@yahoo.com>,
both forms are invalid anyway, and recent versions of Postfix treat them
the same. It is probably a good idea to set strict_rfc821_envelopes=yes
in main.cf to reject such non-replyable sender addresses straight away,
otherwise we end up processing such mail with inability to bounce it when
needed, effectively losing it;


Mark