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As follows, RFC822 refers "Received:" header's "for" parameter as "initial form".
What does "initial form" mean? The word "initial form" is too generic.

received    =  "Received"    ":"            ; one per relay
                       ["from" domain]           ; sending host
                       ["by"   domain]           ; receiving host
                       ["via"  atom]             ; physical path
                      *("with" atom)             ; link/mail protocol
                       ["id"   msg-id]           ; receiver msg id
                       ["for"  addr-spec]        ; initial form
                        ";"    date-time         ; time received
Null Penguin
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1 Answers1

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AFAIK "for" part of Received: header (optionally) provides track of recipient address (at SMTP session level).

AnFi
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  • In my case the address provided here was the postmaster address of recipient domain while the receiveing host provided in "by" was the sender's mail server. So I wonder how and why the postmaster address provided in "for". – Null Penguin Mar 03 '21 at 12:19
  • It should mean that the email was originally addressed to postmaster [ `RCPT TO` in SMTP session] before applying chain of aliases [typically postmaster->root->user-x] – AnFi Mar 03 '21 at 13:26
  • My case has only one recipient. From: bob@example.com, To: alice@example.org. Bob doesn't know the address postmaster@example.org. However, in the header of the message Alice received, "Received" header appears like this; Received: by smtp.example.com / for postmaster@example.org. Why does postmaster@example.org appear? Both bob and alice don't know the address, in addition this email was delivered with no problem. – Null Penguin Mar 04 '21 at 14:34