Re: [PATCH v2] send-email: add an option to impose delay sent E-Mails

[Eric Wong <e@80x24.org>]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
> Add a --send-delay option with a corresponding sendemail.smtpSendDelay
> configuration variable. When set to e.g. 2, this causes send-email to
> sleep 2 seconds before sending the next E-Mail. We'll only sleep
> between sends, not before the first send, or after the last.
> 
> This option has two uses. Firstly, to be able to Ctrl+C a long send
> with "all" if you have a change of heart. Secondly, as a hack in some
> mail setups to, with a sufficiently high delay, force the receiving
> client to sort the E-Mails correctly.
> 
> Some popular E-Mail clients completely ignore the "Date" header, which
> format-patch is careful to set such that the patches will be displayed
> in order, and instead sort by the time the E-mail was received.
> 
> Google's GMail is a good example of such a client. It ostensibly sorts
> by some approximation of received time (although not by any "Received"
> header). It's more usual than not to see patches showing out of order
> in GMail. To take a few examples of orders seen on patches on the Git
> mailing list:
> 
>     1 -> 3 -> 4 -> 2 -> 8 -> 7 (completion by Nguyễn Thái Ngọc Duy)
>     2 -> 0 -> 1 -> 3 (pack search by Derrick Stolee)
>     3 -> 2 -> 1 (fast-import by Jameson Miller)
>     2 -> 3 -> 1 -> 5 -> 4 -> 6 (diff-highlight by Jeff King)
> 
> The reason to add the new "X-Mailer-Send-Delay" header is to make it
> easy to tell what the imposed delay was, if any. This allows for
> gathering some data on how the transfer of E-Mails with & without this
> option behaves. This may not be workable without really long delays,
> see [1] and [2].

Aside from the new header, I think this is better implemented
using the existing $relogin_delay and $batch_size=1.

Disconnecting during the delay might be more sympathetic to
existing mail servers (which aren't C10K-optimized).  If the
client sleeps, the server may disconnect the client anyways
to save resources.

> @@ -1741,6 +1747,10 @@ sub process_file {
>  		$message, $xfer_encoding, $target_xfer_encoding);
>  	push @xh, "Content-Transfer-Encoding: $xfer_encoding";
>  	unshift @xh, 'MIME-Version: 1.0' unless $has_mime_version;
> +	if ($send_delay && $i > 0) {
> +		push @xh, "X-Mailer-Send-Delay: $send_delay";
> +		sleep $send_delay;
> +	}

We can add this header for relogin_delay + batch_size

But maybe --send-delay can be a shortcut for
--relogin-delay and --batch-size=1