[ZendTo] Issues with sending to external users

[Mike Brudenell]

Hi, Brian -

Firstly note that I've not touched Sendmail since 2008 (we use Exim now) so
my memory/interpretation might be hazy in places in my comments below…

On 13 January 2017 at 13:31, Brian Novogradac <Brian.Novogradac at utoronto.ca>
wrote:

> Thanks for helping me out here here is some more information.
>
>
>
> -          Running Centos 6.8
>
> -          Yes the zendto is sending messages to sendmail on the machine
>
> -          I have all hostname information set correctly in hosts file
>
> -          In sendmail.mc I have added the domainname in
> define(`confDOMAIN_NAME', `zendto.host.ca')dnl
>
I seem to remember that you set confDOMAIN_NAME to the domain name you want
adding to unqualified addresses — ie, those that are only a username. If
you have *really* set this to "zendto.host.ca" then a message from/to the
plain username address

apache


say, becomes

apache at zendto.host.ca


I've used dig to look up data for the domain "host.ca" and to be honest I'm
not convinced you've really set it to that as it seems to be something to
do with domainsatcost.ca.


Maillog:
>
>
>
> Jan 13 08:19:19 zendto sendmail[5941]: v0DDJILc005941: from=apache,
> size=1517, class=0, nrcpts=1, msgid=<201701131319.
> v0DDJILc005941 at zendto.XXXXX>, relay=apache at localhost
>

The above will be the locally generated message your apache username is
creating and handing to Sendmail.


Jan 13 08:19:19 zendto sendmail[5942]: v0DDJJOE005942: from=<apache@
> zendto.XXXXX >, size=1744, class=0, nrcpts=1, msgid=<201701131319.
> v0DDJILc005941@ zendto.XXXXX >, proto=ESMTP, daemon=MTA,
> relay=localhost.localdomain [127.0.0.1]
>

Then sendmail qualifies the plain sender address "apache" with a domain
name, making it <apache.zendto.XXXXX> — hmm, if that's the case then that
won't be a valid email address.

I seem to recall that "relay=" identifies the server the message is
transmitted onward to: in this case to the SMTP server running on the same
machine — localhost.localdomain [127.0.0.1]


Jan 13 08:19:19 zendto sendmail[5941]: v0DDJILc005941: to=userXXX at gmail.com,
> ctladdr=apache (48/48), delay=00:00:01, xdelay=00:00:00, mailer=relay,
> pri=31517, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent
> (v0DDJJOE005942 Message accepted for delivery)
>

I think the above is Sendmail logging it has successfully transmitted your
message to the SMTP listener running on your host.



> Jan 13 08:19:20 zendto sendmail[5944]: STARTTLS=client, relay=
> gmail-smtp-in.l.google.com., version=TLSv1/SSLv3, verify=FAIL,
> cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128
>

Your Sendmail then decides it needs to transmit the message to the server
gmail-smtp-in.l.google.com

Which tallies with the MX records for gmail.com — these have the most
preferred one being gmail-smtp-in.l.google.com


Jan 13 08:19:20 zendto sendmail[5944]: v0DDJJOE005942: to=<
> userXXX at gmail.com >, ctladdr=<apache@ zendto.XXXXX > (48/48),
> delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=121744, relay=
> gmail-smtp-in.l.google.com. [IPv6:2607:f8b0:4001:c01::1b], dsn=5.0.0,
> stat=Service unavailable
>

The above line is Gmail's SMTP server refusing to accept your message,
returning a 5xx permanent failure response code, with the rather unhelpful
explanatory text "Service unavailable".

The 5xx response code tells your Sendmail to abandon any further attempts
to send the message and to generate a Non-Delivery Report to return to the
sender.



> Jan 13 08:19:20 zendto sendmail[5944]: v0DDJJOE005942: v0DDJKOE005944:
> DSN: Service unavailable
>
> Jan 13 08:19:20 zendto sendmail[5944]: v0DDJKOE005944: to=root,
> delay=00:00:00, xdelay=00:00:00, mailer=local, pri=32992, dsn=2.0.0,
> stat=Sent
>

This shows a message being delivered to the local mailbox belonging to the
root username on your server — ie, the Zendto box. Check in that mailbox
and you'll likely find the Non-Delivery Report, hopefully with some
information about why the message was rejected by Gmail.

Things that trouble me are the stray spaces everywhere. For example the
sender address seems to be <apache@ zendto.XXXXX > and the recipient
address < userXXX at gmail.com >. But a quick test suggests Gmail would reject
these with a "555 5.5.2 Syntax error." response rather than "Service
unavailable".


Email Header:
>
>
>
> Received: from zendto.XXXXX (localhost.localdomain [127.0.0.1]) by
> zendto.XXXXX t(8.14.4/8.14.4) with ESMTP id v0CJ8WAd001980; Thu, 12 Jan
> 2017 14:08:32 -0500
> Received: (from apache at localhost) by zendto.XXXXX (8.14.4/8.14.4/Submit)
> id v0CJ8Wm9001976; Thu, 12 Jan 2017 14:08:32 -0500
> Date: Thu, 12 Jan 2017 14:08:32 -0500
> Message-ID: <201701121908.v0CJ8Wm9001976@ zendto.XXXXX
> <201701121908.v0CJ8Wm9001976 at send.utoronto.ca>>
> To: < userXXX at gmail.com >
> Subject: User has dropped off a file for you
> X-PHP-Originating-Script: 0:NSSDropbox.php
> From: Zendto <no-reply@ zendto.XXXXX <no-reply at utoronto.ca>>
>

Basically there's still a lot of obfuscation, possibly along with some
typos (the stray spaces) introduced whilst obfuscating, for anyone else to
be sure what's going on. You'll need to discuss your pristine logs with a
local Sendmail support guru at your site.

Cheers,
Mike B.

-- 
Systems Administrator & Change Manager
IT Services, University of York, Heslington, York YO10 5DD, UK
Tel: +44-(0)1904-323811

Web: www.york.ac.uk/it-services
Disclaimer: www.york.ac.uk/docs/disclaimer/email.htm
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