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Re: SMTP relay issue with emails to specific domain

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On 08/09/16 13:56, Daniel Bareiro wrote:

> I recently set up an relay SMTP server on a host of Digital Ocean, using
> Debian and Postfix.
> 
> The main reason for setting up this relay is that the cPanel VPS is
> hosted at Godaddy, and they force everyone to send email through their
> shared SMTP relay. As expected, that shared relay is continually being
> flagged for spam.
> 
> So the outgoing emails are routed through this server. Usually
> everything worked smoothly. Mails to accounts on Google, Yahoo, Hotmail
> and other servers are delivered. But I found a problem with a specific
> domain:
> 
> -----------------------------------------------------------------------
> Sep  7 14:36:11 smtp postfix/smtp[8036]: 5EAA520AAD:
> to=<xxxx@lkeusa.com>, relay=lkeusa.com[50.87.144.56]:25], delay=13,
> delays=0.91/0.06/6.1/5.9, dsn=5.0.0, status=bounced (host
> lkeusa.com[50.87.144.56] said: 550-Please turn on SMTP Authentication in
> your mail client, or login to the 550-IMAP/POP3 server before sending
> your message.  smtp.server.com 550-[x.y.z.t]:41988 is not permitted to
> relay through this server 550 without authentication. (in reply to RCPT
> TO command))
> -----------------------------------------------------------------------
> 
> I'm not sure why this specific domain is complaining in this way.
> 
> Another thing that is strange to me is that apparently a dig query is
> not returning nothing:
> 
> -----------------------------------------------------------------------
> $ dig -t mx lkeusa.com
> 
> ; <<>> DiG 9.9.5-9+deb8u6-Debian <<>> -t mx lkeusa.com
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 31796
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
> 
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags:; udp: 4096
> ;; QUESTION SECTION:
> ;lkeusa.com.                    IN      MX
> 
> ;; Query time: 531 msec
> ;; SERVER: 10.1.0.6#53(10.1.0.6)
> ;; WHEN: Thu Sep 08 13:48:38 ART 2016
> ;; MSG SIZE  rcvd: 39
> -----------------------------------------------------------------------
> 
> But Postfix was trying to deliver the mail in 50.87.144.56.
> 
> Maybe they were making changes to the remote server?

Well, it seems that in the absence of an MX record, Postfix uses the A
record that it find by querying that domain and in that IP address an
Exim server responds:

-----------------------------------------------------------------------
# telnet lkeusa.com 25
Trying 50.87.144.56...
Connected to lkeusa.com.
Escape character is '^]'.
220-gator3037.hostgator.com ESMTP Exim 4.86_1 #1 Thu, 08 Sep 2016
12:15:19 -0500
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
-----------------------------------------------------------------------

But I have not yet determined what the cause of that error 550 which is
not present with other SMTP servers like Gmail.

I will continue investigating. Any comments that shed some more light on
this will be appreciated.


Kind regards,
Daniel

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Thread

SMTP relay issue with emails to specific domain Daniel Bareiro <daniel-listas@gmx.net> - 2016-09-08 19:00 +0200
  Re: SMTP relay issue with emails to specific domain Daniel Bareiro <daniel-listas@gmx.net> - 2016-09-08 19:40 +0200
    Re: SMTP relay issue with emails to specific domain Stephan Beck <sbeck@secure.mailbox.org> - 2016-09-09 20:20 +0200
      Re: SMTP relay issue with emails to specific domain Daniel Bareiro <daniel-listas@gmx.net> - 2016-09-09 21:10 +0200
        Re: SMTP relay issue with emails to specific domain Joe <joe@jretrading.com> - 2016-09-09 22:00 +0200
          Re: SMTP relay issue with emails to specific domain Greg Wooledge <wooledg@eeg.ccf.org> - 2016-09-09 22:20 +0200
            Re: SMTP relay issue with emails to specific domain Joe <joe@jretrading.com> - 2016-09-09 23:10 +0200
              Re: SMTP relay issue with emails to specific domain Daniel Bareiro <daniel-listas@gmx.net> - 2016-09-10 01:20 +0200
        Re: SMTP relay issue with emails to specific domain <tomas@tuxteam.de> - 2016-09-09 22:40 +0200

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