lmtpd NUL rejection

[Igor Brezac]

On Fri, 10 Jan 2003 simon.brady at otago.ac.nz wrote:

> I've recently upgraded imapd from 1.5.19 to 2.1.11, and instead of having
> sendmail invoke deliver it now talks to lmtpd over a Unix socket. All is
> well, except that lmtpd is much more scrupulous about checking its input
> than deliver was - in the space of a week, it's detected three otherwise
> normal messages containing embedded NULs and has rejected them with DSN
> "554 5.6.0 Message contains NUL characters" (status
> IMAP_MESSAGE_CONTAINSNULL in imap/lmtpengine.c).
>
> OK, fair enough, except that sendmail responds to the bounce by trying to
> copy the message to postmaster. Via lmtpd. Oops.
>
> Clearly the input is bad and lmtpd is justified in rejecting it. However,
> broken mail clients (or whatever - we haven't identified any common factor
> yet) are a fact of life, and having mail stuck in a non-delivery loop
> isn't very helpful for our users.
>
> What's the Right Thing to do here? Should sendmail (8.11.2) be configured
> to somehow report the failure without forwarding the message, or perhaps
> do NUL filtering on the fly? Or is there some way of configuring the lmtp
> mailer definition to get around this problem?

Have you tried F=1 mailer flag?  This may only work in Sendmail 8.12.x.

>From op.txt:

1   Don't send null characters ('\0') to this  mailer.

I have not tried this flag yet, so I am not sure if NULL chars are removed
or if the message is rejected.

> And out of general curiosity, have other sites moving to lmtpd encountered
> this, or are we just particularly weird?

This is not new, Cyrus 1.6.x 'deliver' rejects such messages as well.

-- 
Igor