dovecot - Aug 2019 - Feature wishlist: Allow to hide client IP/host in submission service

Hi,

In many mail setups a required feature (for privacy reasons) is to
hide the host and IP of clients (in the "Received" header) that use
the authenticated submission over port 587. In Postfix that's
possible (https://serverfault.com/q/413533/86332), but not very nice
to configure especially if you only want want to strip the Received
header for port 587 submissions, but not on port 25.

As far as I can see this configuration is not possible at all in the
Dovecot submission server because the function which adds the
Received header with the client's IP address
(smtp_server_transaction_write_trace_record) is always called in
submission-commands.c.

It would be very useful if the submission server could anonymize the
client with a single configuration option, then all the Postfix
configuration mess (and using SASL) could be skipped by simply using
the Dovecot submission server instead.

The anonymization would work by replacing the client's EHLO host
with "submission" and the IP address with 127.0.0.1. In full the
Received header would look something like this where the first line
is always the same:

Received: from submission (unknown [127.0.0.1])
   by mail.example.com with ESMTPSA
   id 8bV9D+51Yl1FOwAA1ctoJQ
   (envelope-from <john at example.com>)
   for <jane at example.com>; Sun, 25 Aug 2019 13:50:06 +0200

Sebastian

On 2019-08-25 20:51, Sebastian Krause via dovecot wrote:
> Hi,
> 
> In many mail setups a required feature (for privacy reasons) is to
> hide the host and IP of clients (in the "Received" header) that
use
> the authenticated submission over port 587. In Postfix that's
> possible (https://serverfault.com/q/413533/86332), but not very nice
> to configure especially if you only want want to strip the Received
> header for port 587 submissions, but not on port 25.
> 
> As far as I can see this configuration is not possible at all in the
> Dovecot submission server because the function which adds the
> Received header with the client's IP address
> (smtp_server_transaction_write_trace_record) is always called in
> submission-commands.c.
> 
> It would be very useful if the submission server could anonymize the
> client with a single configuration option, then all the Postfix
> configuration mess (and using SASL) could be skipped by simply using
> the Dovecot submission server instead.
> 
> The anonymization would work by replacing the client's EHLO host
> with "submission" and the IP address with 127.0.0.1. In full the
> Received header would look something like this where the first line
> is always the same:
> 
> Received: from submission (unknown [127.0.0.1])
>    by mail.example.com with ESMTPSA
>    id 8bV9D+51Yl1FOwAA1ctoJQ
>    (envelope-from <john at example.com>)
>    for <jane at example.com>; Sun, 25 Aug 2019 13:50:06 +0200
Check https://github.com/dovecot/core/pull/74

Unsure if it covers Submission though

Tom Sommer <mail at tomsommer.dk> wrote:
> Check https://github.com/dovecot/core/pull/74
>
> Unsure if it covers Submission though
Unfortunately not, the "Received" header is added here and there is
no check for an option:

https://github.com/dovecot/core/blob/25f6146c1e04ae8419fbba30f193332f71945dc4/src/submission/submission-commands.c#L245

On 25 Aug 2019, at 21.51, Sebastian Krause via dovecot <dovecot at
dovecot.org> wrote:
> 
> Hi,
> 
> In many mail setups a required feature (for privacy reasons) is to
> hide the host and IP of clients (in the "Received" header) that
use
> the authenticated submission over port 587. In Postfix that's
> possible (https://serverfault.com/q/413533/86332), but not very nice
> to configure especially if you only want want to strip the Received
> header for port 587 submissions, but not on port 25.
> 
> As far as I can see this configuration is not possible at all in the
> Dovecot submission server because the function which adds the
> Received header with the client's IP address
> (smtp_server_transaction_write_trace_record) is always called in
> submission-commands.c.
> 
> It would be very useful if the submission server could anonymize the
> client with a single configuration option, then all the Postfix
> configuration mess (and using SASL) could be skipped by simply using
> the Dovecot submission server instead.
Yeah, it would be useful to hide the client's IP and do it by default.
Actually I think there shouldn't even be an option to not hide it. Or would
it be better or worse to just not have the Received header added at all?

On 2019-08-28 14:07, Timo Sirainen via dovecot wrote:
> On 25 Aug 2019, at 21.51, Sebastian Krause via dovecot
> <dovecot at dovecot.org> wrote:
>> 
>> Hi,
>> 
>> In many mail setups a required feature (for privacy reasons) is to
>> hide the host and IP of clients (in the "Received" header)
that use
>> the authenticated submission over port 587. In Postfix that's
>> possible (https://serverfault.com/q/413533/86332), but not very nice
>> to configure especially if you only want want to strip the Received
>> header for port 587 submissions, but not on port 25.
>> 
>> As far as I can see this configuration is not possible at all in the
>> Dovecot submission server because the function which adds the
>> Received header with the client's IP address
>> (smtp_server_transaction_write_trace_record) is always called in
>> submission-commands.c.
>> 
>> It would be very useful if the submission server could anonymize the
>> client with a single configuration option, then all the Postfix
>> configuration mess (and using SASL) could be skipped by simply using
>> the Dovecot submission server instead.
> 
> Yeah, it would be useful to hide the client's IP and do it by default.
> Actually I think there shouldn't even be an option to not hide it. Or
> would it be better or worse to just not have the Received header added
> at all?
Better to just remove the Received header entirely.

Make lmtp_add_received_headers work on submission as well, maybe?

> On Aug 28, 2019, at 8:07 AM, Timo Sirainen via dovecot <dovecot at
dovecot.org> wrote:
> 
>> On 25 Aug 2019, at 21.51, Sebastian Krause via dovecot <dovecot at
dovecot.org> wrote:
>> 
>> Hi,
>> 
>> In many mail setups a required feature (for privacy reasons) is to
>> hide the host and IP of clients (in the "Received" header)
that use
>> the authenticated submission over port 587. In Postfix that's
>> possible (https://serverfault.com/q/413533/86332), but not very nice
>> to configure especially if you only want want to strip the Received
>> header for port 587 submissions, but not on port 25.
>> 
>> As far as I can see this configuration is not possible at all in the
>> Dovecot submission server because the function which adds the
>> Received header with the client's IP address
>> (smtp_server_transaction_write_trace_record) is always called in
>> submission-commands.c.
>> 
>> It would be very useful if the submission server could anonymize the
>> client with a single configuration option, then all the Postfix
>> configuration mess (and using SASL) could be skipped by simply using
>> the Dovecot submission server instead.
> 
> Yeah, it would be useful to hide the client's IP and do it by default.
Actually I think there shouldn't even be an option to not hide it. Or would
it be better or worse to just not have the Received header added at all?
> 
The intent of the the Received header is to troubleshoot mail problems, so
having the ability to add it in is important.

My votes would be:

1) The ability to control the content of the Received header.

2) The ability to turn the Received line on or off

Timo Sirainen <timo at sirainen.com> wrote:
> Yeah, it would be useful to hide the client's IP and do it by
> default. Actually I think there shouldn't even be an option to not
> hide it. Or would it be better or worse to just not have the
> Received header added at all?
I don't think it's a good idea to just hide the Received header
completely because it contains useful information to track down mail
problems:

Received: from client.example.com ([1.2.3.4])
    by mail.example.com with ESMTPSA
    id PBjFKTKxZl3AEQAA1ctoJQ
    (envelope-from <sebastian at realpath.org>)
    for <sebastian at realpath.org>; Wed, 28 Aug 2019 18:52:02 +0200

The third line contains the "id" that also shows up in the Dovecot
logs and might be the quickest way to track down users with abusive
behavior (e.g. spammers).

If a configuration option is too much, I think anonymizing by
default is the next best approach, with the first line of the header
being something like this:

Received: from submission ([127.0.0.1])