See here: http://lists-archives.com/git/846970-git-send-email-connection-closed.html for a description of the bug and a workaround:

> > Net::SMTP::SSL=GLOB(0x1fb3558)>>> +MODULE_LICENSE("GPL");
> > Net::SMTP::SSL=GLOB(0x1fb3558)>>> -- 
> > Net::SMTP::SSL=GLOB(0x1fb3558)>>> 2.4.5
> > Net::SMTP::SSL: Net::Cmd::datasend(): unexpected EOF on command channel:
> >  at /usr/lib/git-core/git-send-email line 1320.
> > [Net::SMTP::SSL] Connection closed at /usr/lib/git-core/git-send-email
> > line 1320.
> > 
> > It seems to me that there is a size limit, after cutting down the patch
> > to ~16K, sending started to work. I cut it twice, once by removing lines
> > from the head and once from the bottom, in both cases at the size of
> > around 16K I could send the patch.
> 
> I found a work-around by using datasend line by line, which did the job
> for me:
> 
> Altering /usr/lib/git-core/git-send-email, around line 1320:
> 
>                 $smtp->datasend("$header\n") or die $smtp->message;
>                 my @lines = split /^/, $message;
>                 foreach my $line (@lines) {
>                         $smtp->datasend("$line") or die $smtp->message;
>                 }