Re: [PATCH v5] send-email: --batch-size to work around some SMTP server limit

On Sun, May 21, 2017 at 2:59 PM, xiaoqiang zhao [off-list ref] wrote:

Some email servers (e.g. smtp.163.com) limit the number emails to be
sent per session(connection) and this will lead to a faliure when
sending many messages.

This OK to me, the nits I had are addressed by Junio's reply.

Looking at this the Nth time now though I wonder about this approach
in general. In all your E-Mails I don't think you ever said /what/
sort of error you had from the SMTP server, you just said you had a
failure or an error, I assume you hit one of the die's in the
send_message() function. Can you paste the actual error you get
without this patch?

I wonder if something like this would Just Work for this case without
any configuration or command-line options, with the added benefit of
just working for anyone with transitory SMTP issues as well (patch
posted with -w, full version at
https://github.com/avar/git/commit/acb60c4bde50bdcb62b71ed46f49617e2caef84e.patch):

diff --git a/git-send-email.perl b/git-send-email.perl
index 8a1ee0f0d4..c2d85236d1 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl

@@ -1363,6 +1363,10 @@ EOF
                        die __("The required SMTP server is not

properly defined.")
                }

+               my $num_tries = 0;
+               my $max_tries = 5;
+       smtp_again:
+               eval {
                        if ($smtp_encryption eq 'ssl') {
                                $smtp_server_port ||= 465; # ssmtp
                                require Net::SMTP::SSL;

@@ -1429,6 +1433,22 @@ EOF
                        }
                        $smtp->dataend() or die $smtp->message;
                        $smtp->code =~ /250|200/ or die

sprintf(__("Failed to send %s\n"), $subject).$smtp->message;
+                       1;
+               } or do {
+                       my $error = $@ || "Zombie Error";
+
+                       warn sprintf(__("Failed to send %s due to
error: %s"), $subject, $error);
+                       if ($num_tries++ < $max_tries) {
+                               $smtp->quit if defined $smtp;
+                               $smtp = undef;
+                               $auth = undef;
+                               my $sleep = $num_tries * 3; # 3, 6, 9, ...
+                               warn sprintf(__("This is retry %d/%d.
Sleeping %d before trying again"),
+                                            $num_tries, $max_tries, $sleep);
+                               sleep($sleep);
+                               goto smtp_again;
+                       }
+               };
        }
        if ($quiet) {
                printf($dry_run ? __("Dry-Sent %s\n") : __("Sent
%s\n"), $subject);

Now that's very much a WIP and I don't have a server like that to test against.

Having worked with SMTP a lot in a past life/job, I'd say it's *very*
likely that you're just getting a /^4/ error code from 163.com,
probably 421, which would make this logic even simpler. I.e. we could
just adjust this to back-off for /^4/ instead of trying to handle
arbitrary errors.

Anyway, I'm not interested in pursuing that WIP patch, and I don't
think perfect should be the enemy of the good here. Your patch works
for you, doesn't really damage anything else, so if you're not
interested in hacking up something like the above I think we should
just take it.

But I do think it would be very good to get a reply to you / details
in the commit message about what error you get exactly in this
scenario, see if you get better details with --smtp-debug, and if so
paste that (sans any secret info like user/password you don't want to
share).

Then if we're poking at this code in the future we can maybe just fix
this in some more general fashion while keeping this use-case in mind.