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I received an email and I noticed that the Delivered-To: and To: fields were different. The To: field is not my actual email address, but the Delivered-To: field is. How does this happen?

Delivered-To: mike.smith@work.com
To: "msmith@work.com" <msmith@work.com>

To add to this - I thought there might be some automatic forwarding setup at my office, but I tested sending something to msmith@work.com and it didn't come through to me.

metersk
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asdf
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3 Answers3

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Just like snail mail letters, SMTP email has two different sets of address information: the envelope headers (like the addresses printed on the outside of an envelope) which are used by the SMTP servers to route and deliver the email, and the normal headers, which are part of the mail message and which are only read and interpreted by the user in his mail client/webmail, just like the address attached to a salutation at the start of a physical letter.

Unlike the post office, SMTP usually throws away most of the envelope before it hands the message to the user. I think your Delivered-To: header probably reflects the original RCPT TO: header found in the SMTP envelope.

The To: header is part of the mail message and your address does not need to be there for the message to get delivered correctly. (As long as your address is in the envelope it gets delivered to you.)

You'll find that the case when among others your email gets forwarded or when your address was on the BCC (blind carbon copy) field.

HBruijn
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  • Is Delivered-To a standard header? Why does gmail use it instead of X-Delivered-To – Pacerier Nov 03 '17 at 09:35
  • So are you saying that `RCPT TO` is the standard equivalent of `Delivered-To`? – Pacerier Jan 10 '18 at 13:02
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    No. `RCPT TO:` is the SMTP command. `Delivered-To:` *may* be how the SMTP server at the final destination records to which mailbox the message was sent; after alias expansion, forwards, address rewrites etc. As far as *I know* there is no standard that mandates/defines it. – HBruijn Jan 10 '18 at 13:34
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    @Pacerier The `Delivered-To` header indeed is non-standard, but implemented in a few widely used unix smtps like qmail and postfix. See here http://www.postfix.org/virtual.8.html _sorry for being a little late to the party_ – Kaii May 13 '20 at 21:50
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If its gmail its possible there is a forward or an alias setup. Also I believe if it has either listed for that users mailbox it could report one or the other.

I would suggest verifying Forwarding options are setup correctly after looking to see if either a forward or an alias are setup.

If you send that message to msmith@work.com and it reported mike.smith@work.com I believe that would mean mike.smith@work.com is the ACTUAL mailbox label.

Let us know!

Captain Garry
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  • So I thought there might be some automatic forwarding at my office, but I tested sending something to `msmith@work.com` and it didn't come through to me. – metersk Aug 15 '16 at 16:07
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To: is an initial and mandatory email header. Its value is being used by SMTP servers in order to properly route your mail.
Delivery-to:, in contrast, is not mandatory and is added only when the mail is delivered to mailbox. In some setups this may happen more than once, but usually this is the end of route.
Practically:
- sender sends mail to msmith@work.com
- through MX record it reaches your SMTP server
- aliases table on your SMTP server has an entry which says

Forward all mail for msmith@work.com to mike.smith@work.com

According to this entry, SMTP server delivers mail to mike.smith@work.com mailbox adding Delivered-to: header to the mail or delegates delivery to POP3/IMAP server. There are a lot of ways (except aliases) to change recepient's mailbox name on STMP server. This is common practice which brings ease into mail management and migration.

user1700494
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