What is the behavior difference between return-path reply-to and from

Question

On our mailing application we are sending emails with the following header   FROM  marketing customer com TO  subscriber1 domain1 com Return-PATH  bouncemgmt ourcompany com   The problem that we are facing is that some email servers will bounce back a message immediately and use the from or reverse path  marketing customer com  instead to our bounce mgmt server   We want to know if we modify in the header the reply-to to be the same as the return-path if we will be able to catch all bounces   Any other ideas are welcome   We are using the following documents as references  VERP RFC Bounce Messages  SMTP Log Parsing to get Bounces  EDIT 1  A few more bits of information to see if we can get this resolve     We want to know at what point the email server relaying the message will choose to use the reply-to versus the return-path   We have notice that when the first smtp server relaying the message gets rejected it sends it to the reply-to  but when it happens after one hop it sends it to the return-path

User · Accepted Answer

Let s start with a simple example  Let s say you have an email list  that is going to send out the following RFC2822 content     From   lt coolstuff mymailinglist com gt  To   lt you yourcompany com gt  Subject  Super simple email Reply-To   lt coolstuff-threadId 123 mymailinglist com gt   This is a very simple body     Now  let s say you are going to send it from a mailing list  that implements VERP  or some other bounce tracking mechanism that uses a different return-path    Lets say it will have a return-path of coolstuff-you yourcompany com mymailinglist com  The SMTP session might look like     S 220 workstation1 Microsoft ESMTP MAIL Service  C HELO workstation1  S 250 workstation1 Hello  127 0 0 1   C MAIL FROM  lt coolstuff-you yourcompany com mymailinglist com gt   S 250 2 1 0 me mycompany com    Sender OK  C RCPT TO  lt you yourcompany com gt   S 250 2 1 5 you yourcompany com   C DATA  S 354 Start mail input  end with  lt CRLF gt   lt CRLF gt   C From   lt coolstuff mymailinglist com gt  To   lt you yourcompany com gt  Subject  Super simple email Reply-To   lt coolstuff-threadId 123 mymailinglist com gt   This is a very simple body      S 250 Queued mail for delivery  C QUIT  S 221 Service closing transmission channel    Where  C  and  S  represent Client and Server commands  respectively   The recipient s mail would look like    Return-Path  coolstuff-you yourcompany com mymailinglist com From   lt coolstuff mymailinglist com gt  To   lt you yourcompany com gt  Subject  Super simple email Reply-To   lt coolstuff-threadId 123 mymailinglist com gt   This is a very simple body     Now  let s describe the different  FROM s    The return path  sometimes called the reverse path  envelope sender  or envelope from     all of these terms can be used interchangeably  is the value used in the SMTP session in the MAIL FROM command  As you can see  this does not need to be the same value that is found in the message headers  Only the recipient s mail server is supposed to add a Return-Path header to the top of the email  This records the actual Return-Path sender during the SMTP session  If a Return-Path header already exists in the message  then that header is removed and replaced by the recipient s mail server    All bounces that occur during the SMTP session should go back to the Return-Path address  Some servers may accept all email  and then queue it locally  until it has a free thread to deliver it to the recipient s mailbox  If the recipient doesn t exist  it should bounce it back to the recorded Return-Path value   Note  not all mail servers obey this rule  Some mail servers will bounce it back to the FROM address    The FROM address is the value found in the FROM header  This is supposed to be who the message is FROM  This is what you see as the  FROM  in most mail clients   If an email does not have a Reply-To header  then all human  mail client  replies should go back to the FROM address  The Reply-To header is added by the sender  or the sender s software   It is where all human replies should be addressed too   Basically  when the user clicks  reply   the Reply-To value should be the value used as the recipient of the newly composed email  The Reply-To value should not be used by any server  It is meant for client-side  MUA  use only    However  as you can tell  not all mail servers obey the RFC standards or recommendations   Hopefully this should help clear things up   However  if I missed anything  let me know  and I ll try to answer

User · Answer

Another way to think about Return-Path vs Reply-To is to compare it to snail mail   When you send an envelope in the mail  you specify a return address  If the recipient does not exist or refuses your mail  the postmaster returns the envelope back to the return address  For email  the return address is the Return-Path   Inside of the envelope might be a letter and inside of the letter it may direct the recipient to  Send correspondence to example address   For email  the example address is the Reply-To   In essence  a Postage Return Address is comparable to SMTP s Return-Path header and SMTP s Reply-To header is similar to the replying instructions contained in a letter

User · Answer

for those who got here because the title of the question   I use Reply-To  address with webforms  when someone fills out the form  the webpage sends an automatic email to the page s owner  the From  is the automatic mail sender s address  so the owner knows it is from the webform  but the Reply-To  address is the one filled in in the form by the user  so the owner can just hit reply to contact them

User · Answer

I had to add a Return-Path header in emails send by a Redmine instance  I agree with greatwolf only the sender can determine a correct  non default  Return-Path  The case is the following   E-mails are send with the default email address   admin yourcompany com But we want that the real user initiating the action receives the bounce emails  because he will be the one knowing how to fix wrong recipients emails  and not the application adminstrators that have other cats to whip  -     We use this and it works perfectly well with exim on the application server and zimbra as the final company mail server

[email] What is the behavior difference between return-path, reply-to and from?

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