Re: [tlug] Email forwarding

["Curt J. Sampson" <cjs@example.com>]

On 2022-01-29 16:40 +0100 (Sat), Josh Glover wrote:

> Gmail just silently fails to deliver the mail. It doesn't end up in my
> spam, it just gets /dev/null'd as far as I can tell.

IIRC:

Gmail has two levels of spam detection/prevention. The one people usually
see is where it accepts the mail and marks it as spam, so that it goes into
the spam folder. But Gmail may also refuse to accept a message at SMTP time
(e.g., if it's from an IP address that Gmail considers to be an open
relay). In this case Gmail is not putting the message in /dev/null, but
leaving it up to the sending host to decide what to do with the message.
(It may try to bounce it, /dev/null it, or who knows what.)

You can see this latter action happening in the mail logs in the admin
panel (under Reports » Email Log Search or
https://admin.google.com/ac/emaillogsearch) if you have a paid Google
Workspace account. They've recently changed that logging so that you must
use a search query now, unfortunately, so you can't just see everything
that comes in near-real time, but partial recipient addresses (e.g., just
"cjs") often work reasonably well. (Message-ID searches must match
exactly.)

At https://imgur.com/a/spxNuvv I've posted a couple of images of what the
search screen and results and details for a rejected message look like. The
log seems to indicate that it's returning the following to the sending
server as the reject message (this is the contents of a timestamped action
field; the following one says "Rejected"):

    550-5.7.28 [23.160.193.51 1] Our system has detected an unusual rate of
    550-5.7.28 unsolicited mail originating from your IP address. To protect our
    550-5.7.28 users from spam, mail sent from your IP address has been blocked.
    550-5.7.28 Please visit
    550-5.7.28 <a href="https://support.google.com/mail/?p=UnsolicitedIPError"; target="_blank">https://support.google.com/<wbr>mail/?p=UnsolicitedIPError</a> to review our
    550 5.7.28 Bulk Email Senders Guidelines.

This points out yet another complexity in SMTP; apparently you are now
supposed to support rendering HTML in SMTP responses, including opening a
new tab/window. :-/

An accepted message will of course have log entries for things like:

    Jan 31, 2022, 2:00:27 AM    Received from an SMTP server with IP address: 161.38.200.89 (TLS enabled)
                                250 2.0.0 OK
    Jan 31, 2022, 2:00:27 AM    Inserted into Gmail delivery pipeline
    Jan 31, 2022, 2:00:27 AM    Delivered to Gmail mailbox
                                No Error

and also a "Post-delivery message details" section that tells you where it
is (e.g., in Trash), any labels that have been assigned, whether it's been
seen and possibly opened and read, and so on.

cjs
-- 
Curt J. Sampson      <cjs@example.com>      +81 90 7737 2974

To iterate is human, to recurse divine.
    - L Peter Deutsch