SMTP: Right way to use BCC and To field?

aki · 2 Nov 2007, 07:46 PM

Hi.

I am developing a piece of code that sends an email to a group of email addresses using SMTP. I am sending a 'RCPT TO:' for every email address and to hide the address of every user to the rest I am using header 'To:' in DATA section. But my question is, what's better to use in this header, a fake email address or something like 'unspecified-domain'?
I would like to be as polite as posible to avoid be tagged as 'spammer'.
I am using Postfix like SMTP server.

Thanks in advance.
Aki

Scott Kitterman · 2 Nov 2007, 10:52 PM

The best thing to do is to create one message per recipient with a normal To. That way it will appear to be to them and not show other addresses.

aki · 3 Nov 2007, 02:29 AM

Thanks for your answer, Scott.

But we are sending the message to a set of three generic email addresses, those are mail-groups, so they expand to hundreds of real email adresses, those are not controlled/managed by us. We only know the three generic email addresses, and we don't want to publish this email addresses. That's the reason we cannot send to every email address.

Any suggestion about what's the better way to use "To:" header?

Regards,
Aki

Scott Kitterman · 3 Nov 2007, 11:19 PM

Does the expander rewrite To: anyway? They often do.

lavabit · 8 Nov 2007, 04:32 AM

The proper way, IMO, would be to include your address (or the MAIL FROM) address in the To field. So the SMTP session would look like:

S: 220 lavabit.com ESMTP dispatchd
C: EHLO sender.lavabit.com
S: 250-lavabit.com
S: 250-STARTTLS
S: 250-AUTH LOGIN PLAIN
S: 250-AUTH=LOGIN PLAIN
S: 250 Okay.
C: MAIL FROM: <noreply@lavabit.com>
S: 250 Sender okay.
C: RCPT TO: <user1@example.com>
S: 250 Recipient okay.
C: RCPT TO: <user2@example.com>
S: 250 Recipient okay.
C: DATA
S: 354 Enter mail, end with "." on a line by itself.
C: From: "Mailer Application" <noreply@lavabit.com>
C: To: "Mailer Application" <noreply@lavabit.com>
C: Subject: Were the greatest ever!
C: Date: Wed, 7 Nov 2007 10:04:09 -0600
C:
C: Just announcing to the world via a massive BCC that we
C: are the greatest ever.
C:
C:
C: .
S: 250 Message Accepted.
C: QUIT
S: 221 Bye.

You could technically use Undisclosed-recipients:; in the To header, but I think it looks bad, and confuses users.

2 Nov 2007, 07:46 PM	#1
aki Junior Member Join Date: Apr 2002 Posts: 18	SMTP: Right way to use BCC and To field? Hi. I am developing a piece of code that sends an email to a group of email addresses using SMTP. I am sending a 'RCPT TO:' for every email address and to hide the address of every user to the rest I am using header 'To:' in DATA section. But my question is, what's better to use in this header, a fake email address or something like 'unspecified-domain'? I would like to be as polite as posible to avoid be tagged as 'spammer'. I am using Postfix like SMTP server. Thanks in advance. Aki Last edited by aki : 2 Nov 2007 at 08:17 PM.

2 Nov 2007, 10:52 PM	#2
Scott Kitterman Essential Contributor Join Date: Sep 2006 Location: Ellicott City, MD, USA Posts: 206 Representative of: ControlledMail.com	The best thing to do is to create one message per recipient with a normal To. That way it will appear to be to them and not show other addresses.

3 Nov 2007, 02:29 AM	#3
aki Junior Member Join Date: Apr 2002 Posts: 18	Thanks for your answer, Scott. But we are sending the message to a set of three generic email addresses, those are mail-groups, so they expand to hundreds of real email adresses, those are not controlled/managed by us. We only know the three generic email addresses, and we don't want to publish this email addresses. That's the reason we cannot send to every email address. Any suggestion about what's the better way to use "To:" header? Regards, Aki

3 Nov 2007, 11:19 PM	#4
Scott Kitterman Essential Contributor Join Date: Sep 2006 Location: Ellicott City, MD, USA Posts: 206 Representative of: ControlledMail.com	Does the expander rewrite To: anyway? They often do.

8 Nov 2007, 04:32 AM	#5
lavabit Member Join Date: Mar 2007 Posts: 56 Representative of: Lavabit.com	The proper way, IMO, would be to include your address (or the MAIL FROM) address in the To field. So the SMTP session would look like: S: 220 lavabit.com ESMTP dispatchd C: EHLO sender.lavabit.com S: 250-lavabit.com S: 250-STARTTLS S: 250-AUTH LOGIN PLAIN S: 250-AUTH=LOGIN PLAIN S: 250 Okay. C: MAIL FROM: <noreply@lavabit.com> S: 250 Sender okay. C: RCPT TO: <user1@example.com> S: 250 Recipient okay. C: RCPT TO: <user2@example.com> S: 250 Recipient okay. C: DATA S: 354 Enter mail, end with "." on a line by itself. C: From: "Mailer Application" <noreply@lavabit.com> C: To: "Mailer Application" <noreply@lavabit.com> C: Subject: Were the greatest ever! C: Date: Wed, 7 Nov 2007 10:04:09 -0600 C: C: Just announcing to the world via a massive BCC that we C: are the greatest ever. C: C: C: . S: 250 Message Accepted. C: QUIT S: 221 Bye. You could technically use Undisclosed-recipients:; in the To header, but I think it looks bad, and confuses users.