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Re: FORMS, validating mail was sent

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Gordon Burditt wrote:

>>> + Your mail was dropped on the floor for having an invalid
>>> From: address.  Valid From: addresses likely include ONLY
>>> those with the host name of the server you are sending
>>> from and a known valid user on that system.  Typically
>>> only a few users like root can send mail with 'fake'
>>> (off-system) From: addresses.  Hint: Do NOT put a
>>> user-supplied email address in the From: header.
>> 
>> Utter nonsense.  By that logic, Web-mail like GMail could not possibly
>> work, and it would not be possible to have large e-mail providers in the
>> first place (because the host name of their servers very likely differs
>> from the domain of the From header field address).
> 
> I certainly hope that a self-described "near newbie" is not going to try
> to implement something of the scale of Gmail.
> 
> A self-described "near newbie" is not going to know all the issues
> in properly validating things that go into mail headers.  I won't
> encourage them to put up email forms (or try do-it-yourself parachute
> packing and skydiving) until they learn more.

That the person you are advising is not knowledgable is not an excuse for 
your misinformation.
 
>> Valid From addresses include all that meet the Address Specification in
>> RFC 5322, instead.  This is a purely *syntactical* determination.  It is
>> the fact that even addresses for which there are no mailboxes at the
>> sending server can be used in the From header field value, and that
>> afterwards checking of addresses is unreliable, that allows spammers to
>> thrive.
> 
> From the point of view of sendmail, which is used by default setups in PHP
> (except for Windows), there are other requirements.  Sendmail doesn't like
> local users to forge mail in the name of other users.

Nonsense.
 
>> One must differentiate between the address used as parameter for the MAIL
>> FROM (SMTP) command (the “Envelope-From”), and the “From” Internet
>> message
>> header field.  The latter can be anything; the former can, in theory, be
>> anything unless the *sending* MTA enables counter-measures.  It is not
> 
> For many default setups, the sending MTA enables countermeasures.  This
> can be turned off but not if you are stuck with an unsophisticated hosting
> company that likes to leave settings at the default.
> 
> For some, the receiving MTA enables countermeasures and checks *BOTH* the
> From: line and the envelope sender to the extent that it can (which
> usually means that the domain exists, has an MX or A record, and it
> doesn't point to 127.0.0.1.

Utter nonsense.  An (standards-compliant) “MX” or “A” DNS record *never* 
points to 127.0.0.1.  In particular, an MX record never has an IP address as 
its value, as I have already pointed out.

127.0.0.1 is specified at most in the local host file, and resolving a 
domain name of a supposed e-mail address will *never* result in 127.0.0.1.

> However, if the MTA also hosts the sender domain, the
> check can verify the mailbox exists).

Evidently now you have no clue what you are talking about.
 
> Exim also has "sender verify" (which can be optionally enabled).
> On starting to receive an incoming message, Exim starts to send a
> bounce message back to the envelope-sender.  If the bounce message
> is refused (at the MAIL FROM: and RCPT TO: stage), so is the message.
> The bounce message is never completely sent (and has no text) so
> it's never delivered.  If sender DNS or mail server goes down, the
> message goes nowhere.

That is the counter-measure I was talking about.  It does not pertain to the 
“From” header field, but to the *Envelope*-From.  Which is something that 
you cannot change with PHP's mail().
 
>> possible to change the Envelope-From with simple PHP commands like mail()
>> as that is determined by the MTA (like sendmail) used by the PHP
>> executable.
>  
>> The only good part of this answer is the notion that you invite spammers
>> if you let the end user specify the From header field address without
>> authentification; so you should not do that, indeed.  The /modus
>> operandi/ of spammers and phishers is to harvest or buy e-mail addresses
>> from various sources and use them also in the “From” header field value
>> to make the message look to the recipient like a legitimate e-mail (at
>> first).  This kind of network abuse is also supported by “open relays” –
>> MTAs that would accept and transfer mail for any MAIL FROM to any RCPT
>> TO.
> 
> They also use header injection, so that poorly written contact forms
> can be misused (like an open relay) to send to lots more victims
> than just the webmaster of the site.  Spammers like that even if
> they can't control the From: line.

There is the Suhosin patch and PHP 5.4 against that.

>>> + The intended recipient has a slow DNS server.  If you
>>> send emails to 100 recipients at a time, it is likely
>>> that at least a couple of them have slow DNS servers or
>>> overloaded mail servers.  The mail will stay in the queue
>>> until the message has been delivered to all recipients,
>>> and that can take days, even if 98 of them were delivered
>>> in the first minute.
>> 
>> Utter nonsense.  DNS is only used to resolve the target host of the
>> message, specifically to retrieve the host name from the “MX” or
>> “A”/“AAAA” record of the target domain, and subsequently to resolve the
>> IP address for that host name from its “A” or “AAAA” record (this
>> double-handshake is intended as a
>> safety feature of DNS/SMTP: there must be a host *name* for an MX). 
>> There are no DNS servers anywhere that have a respond time of minutes
>> that would
> 
> I suggest that nobody would know that, since software doesn't wait
> that long for a response - it just gets treated as a nonresponse.

My chkmadd(1) has been treated to a number of Usenet Froms over 10 years to 
talk SMTP to MTAs automatically for checking whether they are munged, and 
never ever has a DNS request timed out.

> However, there are a fair number of DNS servers that don't answer,
> perhaps because they are on the far end of a loaded DSL line.  At
> any given time there are DNS servers that are down or unreachable
> because of hardware failure, loss of network connectivity, or power
> failure.

Name one.

> [more nonsense]

ISTM you need professional help.


PointedEars
-- 
Anyone who slaps a 'this page is best viewed with Browser X' label on
a Web page appears to be yearning for the bad old days, before the Web,
when you had very little chance of reading a document written on another
computer, another word processor, or another network. -- Tim Berners-Lee

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FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-20 13:40 -0400
  Re: FORMS, validating mail was sent Jerry Stuckle <jstucklex@attglobal.net> - 2013-06-20 13:53 -0400
  Re: FORMS, validating mail was sent "J.O. Aho" <user@example.net> - 2013-06-20 20:18 +0200
  Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-20 19:24 +0100
    Re: FORMS, validating mail was sent Jerry Stuckle <jstucklex@attglobal.net> - 2013-06-20 14:40 -0400
    Re: FORMS, validating mail was sent gordonb.vb4vo@burditt.org (Gordon Burditt) - 2013-06-20 14:44 -0500
      Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-20 22:03 +0100
      Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-21 14:06 -0400
      Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-22 11:42 -0400
      Re: FORMS, validating mail was sent Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-23 13:13 +0200
        Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-23 12:22 +0100
          Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-23 13:07 -0400
        Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-23 13:00 -0400
          Re: FORMS, validating mail was sent "J.O. Aho" <user@example.net> - 2013-06-23 20:22 +0200
            Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-23 14:53 -0400
        Re: FORMS, validating mail was sent gordonb.4qaft@burditt.org (Gordon Burditt) - 2013-06-24 14:43 -0500
          Re: FORMS, validating mail was sent "Peter H. Coffin" <hellsop@ninehells.com> - 2013-06-24 15:09 -0500
          Re: FORMS, validating mail was sent Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-25 15:19 +0200
            Re: FORMS, validating mail was sent Jerry Stuckle <jstucklex@attglobal.net> - 2013-06-25 10:11 -0400
              Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-25 11:43 -0400
            Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-25 11:32 -0400
            Re: FORMS, validating mail was sent gordonb.htsnc@burditt.org (Gordon Burditt) - 2013-06-27 10:57 -0500
              Re: FORMS, validating mail was sent Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-27 21:13 +0200
            Re: FORMS, validating mail was sent Arno Welzel <usenet@arnowelzel.de> - 2013-06-28 11:43 +0200
  Re: FORMS, validating mail was sent gordonb.k0cb7@burditt.org (Gordon Burditt) - 2013-06-20 15:46 -0500
    Re: FORMS, validating mail was sent Jerry Stuckle <jstucklex@attglobal.net> - 2013-06-20 17:03 -0400
      Re: FORMS, validating mail was sent gordonb.udxst@burditt.org (Gordon Burditt) - 2013-06-21 19:26 -0500
        Re: FORMS, validating mail was sent Jerry Stuckle <jstucklex@attglobal.net> - 2013-06-21 20:36 -0400
      Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-22 12:04 -0400
    Re: FORMS, validating mail was sent Christoph Michael Becker <cmbecker69@arcor.de> - 2013-06-20 23:39 +0200
      Re: FORMS, validating mail was sent Tim Streater <timstreater@greenbee.net> - 2013-06-21 10:11 +0100
        Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-21 11:25 +0100
          Re: FORMS, validating mail was sent Tim Streater <timstreater@greenbee.net> - 2013-06-21 12:27 +0100
            Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-21 17:59 +0100
              Re: FORMS, validating mail was sent Tim Streater <timstreater@greenbee.net> - 2013-06-21 18:25 +0100
                Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-21 23:43 +0100
                Re: FORMS, validating mail was sent Tim Streater <timstreater@greenbee.net> - 2013-06-22 13:45 +0100
          Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-22 12:20 -0400
    Re: FORMS, validating mail was sent "Peter H. Coffin" <hellsop@ninehells.com> - 2013-06-20 17:27 -0500
      Re: FORMS, validating mail was sent The Natural Philosopher <tnp@invalid.invalid> - 2013-06-21 07:57 +0100
    Re: FORMS, validating mail was sent Twayne <nobody@spamcop.net> - 2013-06-22 12:02 -0400
  Re: FORMS, validating mail was sent GravyCode <matty023@gmail.com> - 2013-06-21 11:30 -0700

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