Synapse smtpsend and blind copies
lazarus / 38-Networking and Web Programming

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ProgEd · 2013-07-21 18:03

I'm developing an application that needs to send email to a rather
sizable list of people, but they all need to be blind copies (BCC).
I've read the "How To" on the synapse web site, but still don't
understand how to send a blind copy.

Can anyone provide a piece of example code that demonstrates how to do
this?

Thanks,
Ed

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ludob · 2013-07-22 04:17

http://synapse.ararat.cz/doku.php/public:howto:sendingbcc

So you take the procedure in
http://synapse.ararat.cz/doku.php/public:howto:smtpsend
and drop the line
Code: [Select]   msg_lines.Insert(1, 'To: ' + sTo);
If you are not interested in TLS then drop the StartTLS.

You should remember that in SMTP, the DATA part is not relevant. Only
email clients interprete the From:, To:, Cc:,  Bcc headers. SMTP
doesn't care at all.


Instead of dropping the To: header it is better to replace it with a
nice name such as 'VIP list' or whatever. Mails without a To: are
displayed in some email clients with "To undisclosed recipients" or
equivalent whcih is a good recipe to get immediately in the spam box.
By the way, mails where the recipient is not in the To: or Cc: header
are also being blocked more and more by spam filters. So Bcc is on its
way out, as it should be.

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ProgEd · 2013-07-22 10:31

Thank you for your prompt reply.

I was aware of problems with not having a recipient in the To: field,
and the application will always have one (the request originator). The
problem is that either it sends multiple emails to the recipients or
we use BCC: since the recipients are competitors and we don't want
them knowing who else is on the list of competitors.

Ed

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ProgEd · 2013-08-06 00:17

Okay, I'm getting very frustrated. I've tried to do what has been
specified, but it doesn't seem to be working. The BCC field is
appearing in the source of the message (doing a view source), but
nothing is being sent to them. Here's the code I'm using:
Code: [Select]      try
         sMsg.Add(Msg);
         sMsg.Insert(0, 'Subject: ' + Subject);
         sMsg.Insert(1, 'From: ' + sEMCont);
         sMsg.Insert(2, 'To: ' + MailTo);
         sMsg.Insert(3, 'Bcc: ' + Vendors);
         sMsg.Insert(4,CRLF);

         smtp.UserName := sEMUID;
         smtp.Password := sEMPWD;
         smtp.TargetHost := sEMSrvr;
         smtp.TargetPort := '25';

         smtp.Login();
         smtp.MailFrom(sEMCont, Length(sEMCont));
         smtp.MailTo(MailTo);
         smtp.MailData(sMsg);
         smtp.Logout();
      finally
         sMsg.Free;
         smtp.Free;
      end;
Any idea what I'm doing wrong?

Thanks,
Ed

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ludob · 2013-08-06 04:48

I can't but repeat myself:
Quote from: ludob on July 22, 2013, 06:17:13 amYou should remember
that in SMTP, the DATA part is not relevant. Only email clients
interprete the From:, To:, Cc:,  Bcc headers. SMTP doesn't care at
all.
What you have done here is just adding the Bcc to the header so that
it is indeed visible for everybody that looks at the source. What you
haven't done is instruct smtpsend to send it to the bcc recipients.

So:
- drop that Bcc line
- replace the line Code: [Select]smtp.MailTo(MailTo); with a loop
where you execute that line for every recipient. That is every
recipient listed in To, Cc and those you want to Bcc. Only one
recipient is allowed per MailTo. See
http://tools.ietf.org/html/rfc5321#section-4.1.1.3 for the relevant
part of the SMTP spec.

If you have more than 100 recipients you should split the recipients
and send the message several times. ie repeat your whole procedure
with the same message but for different sets of recipients. See
http://tools.ietf.org/html/rfc5321#section-4.5.3.1.10 for the error
message you are getting when you exceed the number of permittted
recipients.

EDIT: what you are confusing is the tranfer protocol (SMTP) and the
content that is transfered. The content is for the email client and
goes into smtp.MailData. SMTP is the protocol that delivers the mail.
It is comparable to HTTP (transfer)  and HTML (contents). Both are
completely unrelated.  Bcc is a mail client concept and doesn't exist
for SMTP. SMTP only transfers to a recipient specified in RCPT. If you
don't want a recipient to be visible, you just don't put it in the
message. SMTP doesn't care what goes in your message. Put a 'To: 
Roger.Rabbit@acme.com' in your message and set RCPT to
'Daffy.Duck@acme.com', only Daffy Duck will receive the message. 
Note that this is purely from a protocol perspective. The spam filters
on the receivers end will look at the message content, compare RCPT to
what is in the To:, Cc: sometimes Bcc: headers, etc, to decide if they
deliver or not. But that has nothing to do with the SMTP protocol.

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ProgEd · 2013-08-06 14:18

Thank you. What you suggested is precisely what I had planned to do if
there was no solution to my perceived problem. That, of course, does
work.  Only the original "To:" address shows up in the headers, none
of the other addresses appear, and yet the mail gets to them
correctly.

I am in your debt!

Ed

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Gys · 2013-08-28 21:28

My eye fell accidentally on this thread. A bit late, but still you
might find my post useful:
http://forum.lazarus.freepascal.org/index.php/topic,21900.0.html