Generating a delivery report on the sending system
Jeremy Begg
I'd like to have a web form attempt to validate an email address as part of
the form processing. I'd prefer not to have to implement an SMTP client in
my code, so I wondered if this might be done another way. It doesn't matter
if there's a lengthy delay in the back-end processing of the form.
What I had in mind was for the form processor to send a short message to the
specified email address. (Yes I know this might result in some blow-back
spam on 3rd parties.) If PMDF then finds that the message is undeliverable
it will generate an NDR which my back-end processing can deal with.
The problem is what happens when the email is successfully sent, i.e. PMDF's
SMTP client successfully forwards the mail to an up-stream system? (Or even
to a local email address.)
Is there some way to get the PMDF SMTP client to generate a successful delivery
report? (Or any other PMDF channel, for that matter.)
(This is probably as half-baked as some of my other ideas but it doesn't
hurt to ask!)
Thanks,
Jeremy Begg
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Tom Wade
> What I had in mind was for the form processor to send a short message to the
> specified email address. (Yes I know this might result in some blow-back
> spam on 3rd parties.) If PMDF then finds that the message is undeliverable
> it will generate an NDR which my back-end processing can deal with.
>
> The problem is what happens when the email is successfully sent, i.e. PMDF's
> SMTP client successfully forwards the mail to an up-stream system? (Or even
> to a local email address.)
> Is there some way to get the PMDF SMTP client to generate a successful delivery
> report? (Or any other PMDF channel, for that matter.)
You can request delivery receipts when submitting the message, but there
is no guarantee that they will be provided by the destination mailers.
Since you would be writing code to parse incoming messages, why not do
the following ?
- the web form generates a random token and sends a mail message to the
address with the token at the end of the subject line. The message asks
the user to confirm the operation by replying to the message
- the web form also advises the user to expect such a message.
- when the incoming reply arrives, you search the subject for the token
and complete the validation for that request.
(This is similar to the logic used by MAILSERV's $K option).
The advantage is that you not only check that the address is valid, but
that the person entering the form has read access to that mailbox. Of
course, if that is not the case, it won't work.
The alternative is to have your code
- do an MX lookup on the address (and an A lookup if that doesn't exist).
- make a connection on port 25 and do a HELO/MAIL FROM/RCPT TO sequence
(no need to go any further).
If you get a 2xx response the address probably exists, whereas if the
DNS lookup fails it most likely does not. This does not verify that the
poster has any connection with the address. Not a complete SMTP client,
but it does need some socket coding.
Hope this helps
---------------------------------------------------------
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Ireland
Jeremy Begg
>> What I had in mind was for the form processor to send a short message to the
>> specified email address. (Yes I know this might result in some blow-back
>> spam on 3rd parties.) If PMDF then finds that the message is undeliverable
>> it will generate an NDR which my back-end processing can deal with.
>>
>> The problem is what happens when the email is successfully sent, i.e. PMDF's
>> SMTP client successfully forwards the mail to an up-stream system? (Or even
>> to a local email address.)
>
>> Is there some way to get the PMDF SMTP client to generate a successful delivery
>> report? (Or any other PMDF channel, for that matter.)
>
>You can request delivery receipts when submitting the message, but there
>is no guarantee that they will be provided by the destination mailers.
Hence my interest in having the PMDF SMTP client generate something similar.
A "handoff" report.
..
>The alternative is to have your code
>
>- do an MX lookup on the address (and an A lookup if that doesn't exist).
>- make a connection on port 25 and do a HELO/MAIL FROM/RCPT TO sequence
>(no need to go any further).
>
>If you get a 2xx response the address probably exists, whereas if the
>DNS lookup fails it most likely does not. This does not verify that the
>poster has any connection with the address. Not a complete SMTP client,
>but it does need some socket coding.
Yes, this was my first thought. I just didn't want to write the code :-)
Regards,
Jeremy Begg
ned+in...@mauve.mrochek.com
> > What I had in mind was for the form processor to send a short message to the
> > specified email address. (Yes I know this might result in some blow-back
> > spam on 3rd parties.) If PMDF then finds that the message is undeliverable
> > it will generate an NDR which my back-end processing can deal with.
> >
> > The problem is what happens when the email is successfully sent, i.e. PMDF's
> > SMTP client successfully forwards the mail to an up-stream system? (Or even
> > to a local email address.)
> > Is there some way to get the PMDF SMTP client to generate a successful delivery
> > report? (Or any other PMDF channel, for that matter.)
> You can request delivery receipts when submitting the message, but there
> is no guarantee that they will be provided by the destination mailers.
Actually there is, or at least there's supposed to be.
The theory of operation behind the DSN extension developed by the NOTARY IWTF
WG is that when a SUCCESS report is requested you're _always_ supposed to get a
response back. It may only be a "message tranferred to a system that doesn't
support DSNs" sort of report, but you're supposed to at least get that. Any
agent that fails to provide this is quite simply incompliant.
Of course the spam problem has led a lot of sites to silently drop mail,
including any receipt requests that are attached. I actually don't have a
problem with that. I have a big problem, however, with delivering mail you've
decided isn't spam and not following the rules.
Ned