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

>
> 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].
>
> The reason for why the getopt format is "send-delay=s" instead of
> "send-delay=d" is because we're doing manual validation of the value
> we get passed, which getopt would corrupt in cases of e.g. float
> values before we could show a sensible error message.
>
> 1. https://public-inbox.org/git/20180325210132.GE74743@genre.crustytoothpaste.net/
> 2. https://public-inbox.org/git/xmqqpo3rehe4.fsf@gitster-ct.c.googlers.com/
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>
> I submitted this back in March hoping it would solve mail ordering
> problems, but the other motive I had for this is that I'm paranoid
> that I'm sending out bad E-Mails, and tend to "y" to each one because
> "a" is too fast.'