A way to incrementally upload a maildir to gmail's IMAP servers. Originally by Andreas Kammlott, with some changes

uploadmaildir.pl

#!/usr/bin/perl
# by Andreas Kammlott, thanks to perl and its community

use IO::Socket::SSL;
use Data::Dumper;
use HTTP::Date qw(str2time);
use HTTP::Date qw(parse_date);
use Date::Format;
use Mail::IMAPClient;
use Mail::Box::Maildir;
use Mail::Message::Convert::MailInternet;

# Open imap connection, adjust values to your needs
my $imap = Mail::IMAPClient->new(
   User     => 'username',
   Password => 'password',
   Socket=>IO::Socket::SSL->new(Proto=>'tcp',
   				PeerAddr=>'imap.gmail.com',
				PeerPort=>993)
		) || die "Could not connect to IMAP server.\n";

# A maildir contains a subdir "cur"
foreach my $dir (`find ./ -type d -name cur|sort`) {
   my $imdir = "Inbox"; # to store the path on the server (imap-directory)
   my $fsdir = ""; # to store the path of the maildir (filesystem)

   # Bring the path to an array, each directory needs to be handled
   my @fspath = split(/\//, $dir);

   # Replace the leading point and the tailing .directory to acquire
   # the path, which has to be created in imap, the "cur" don't need
   # to be stored
   for (my $i = 1; $i < @fspath-1; $i++) {
      $fsdir = "$fsdir$fspath[$i]/";
      if ($fspath[$i] =~ /\..*\.directory/) {
         $fspath[$i] =~ s/^\.(.+)\.directory$/$1/;
      }
      #$imdir = "$imdir$fspath[$i]/";
   }

   # Create the mdir object, this object contains all the messages from 
   # the filesystem's maildir
   my $mdir = Mail::Box::Maildir->new(folder => $fsdir, access => 'rw') 
      or print "Failed to create mdir object from \"$fsdir\"\n";

   # Process this directory only if it contains messages
   if (!$mdir->messages() > 0) {
      #print "Skipping... folder has been detected as empty.\n";
      next;
   }

#print Dumper($imap->xlist_folders or die "could not get folder $!");
#exit;

  # Check for the folder on the server (imap) and create if necessary
   if (!$imap->exists($imdir)) {
      # Jump to next folder if creation of this one fails
      if (!$imap->create($imdir)) { 
         print "ERROR: Could not create folder \"$imdir\".\n"; 
         next;
      }
   }

   # Now begin to push all messages
   foreach my $msg ($mdir->messages()) {
	   if ($msg->label(seen) eq 0) {
      my $subject = $msg->subject;
      my $msgdate = $msg->head->get('Date');
      my $msgid   = $msg->messageId;
	   print $subject." - ".$msgid."\n";

      # Required date as RFC2060  dd-Mon-yyyy hh:mm:ss +0000
      # Provided format is Tue, 20 Jul 2004 09:55:16 +0200
      my $time = str2time($msgdate);
      (undef, undef, undef, undef, undef, undef, $tz) = parse_date($msgdate);
      my $date = time2str("%d-%h-%Y %H:%M:%S %z",$time,$tz) 
          or print "problem with time: $time and tz: $tz\n";

      # Create a converter object
      my $conv = Mail::Message::Convert::MailInternet->new;

      # Don't understand why the $conv->export($msg)->as_string() has to be called twice!
      my $exp = $conv->export($msg)->as_string();
	  if (!$imap->append_string($imdir, $conv->export($msg)->as_string(), undef, $date)) {
	     print "Failed to append message!\n"
	          ."ID:$msgid\n"
	          ."SUBJECT:$subject\n"
	          ."IMAPDIR:$imdir\n"
	          ."MESSAGEDATE:$msgdate\n"
	          ."IMPORTDATE:$date\n\n";
	  } else {
		  # Delete the message now that we've uploaded it.
		  $msg ->label(seen => 1)
	  }
  }
   }
}
$imap->close();