What s the difference between Sender From and Return-Path

Question

What s the difference between an email Sender  From and Return-Path value   Example  I have a contact form where the user can input their email  would this be assigned to sender  from or return-path   I had a quick search on the StackOverflow and couldn t find anything useful

User · Accepted Answer

So  over SMTP when a message is submitted  the SMTP envelope  sender  recipients  etc   is different from the actual data of the message     The Sender header is used to identify in the message who submitted it   This is usually the same as the From header  which is who the message is from   However  it can differ in some cases where a mail agent is sending messages on behalf of someone else   The Return-Path header is used to indicate to the recipient  or receiving MTA  where non-delivery receipts are to be sent     For example  take a server that allows users to send mail from a web page   So  sender yourcompany com types in a message and submits it   The server then sends the message to its recipient with From set to sender yourcompany com   The actual SMTP submission uses different credentials  something like mailagent mywebmail com   So  the sender header is set to mailagent mywebmail com  to indicate the From header doesn t indicate who actually submitted the message   In this case  if the message cannot be sent  it s probably better for the agent to receive the non-delivery report  and so Return-Path would also be set to mailagent mywebmail com so that any delivery reports go to it instead of the sender   If you are doing just that  a form submission to send e-mail  then this is probably a direct parallel with how you d set the headers

User · Answer

A minor update to this  a sender should never set the Return-Path  header  There s no such thing as a Return-Path  header for a message in transit  That header is set by the MTA that makes final delivery  and is generally set to the value of the 5321 From unless the local system needs some kind of quirky routing   It s a common misunderstanding because users rarely see an email without a Return-Path  header in their mailboxes  This is because they always see delivered messages  but an MTA should never see a Return-Path  header on a message in transit  See http   tools ietf org html rfc5321 section-4 4

User · Answer

The official RFC which defines this specification could be found here  http   tools ietf org html rfc4021 section-2 1 2  look at paragraph 2 1 2  and the following   2 1 2  Header Field  From Description        Mailbox of message author           Related information      Specifies the author s  of the message  that is  the mailbox es      of the person s  or system s  responsible for the writing of the     message  Defined as standard by RFC 822   2 1 3  Header Field  Sender Description        Mailbox of message sender           Related information      Specifies the mailbox of the agent responsible for the actual     transmission of the message   Defined as standard by RFC 822   2 1 22  Header Field  Return-Path Description      Message return path         Related information      Return path for message response diagnostics  See also RFC 2821      17   Defined as standard by RFC 822

[email] What's the difference between Sender, From and Return-Path?

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