In case someone else has the same question - this is a little script I hacked together myself. Use it at your own risk - as it was used just to migrate stuff it comes without much error checking and no guarantee of not breaking a lot of things...
#!/usr/bin/perl
use strict;
use warnings;
use EBox;
use EBox::Samba::User;
use EBox::MailAliasLdap;
use EBox::Global;
EBox::init();
my $malias = $ARGV[0];
my $myuser = $ARGV[1];
my $mymail = $ARGV[2];
my $users = EBox::Global->modInstance('users');
my $mailAliasLdap = EBox::MailAliasLdap->new();
my $user = EBox::Samba::User->new(samAccountName => $myuser );
if(($mailAliasLdap->aliasExists($malias)))
{
print "$malias belongs to @{$mailAliasLdap->accountsByAlias($malias)} \n";
}
else
{
$mailAliasLdap->addUserAlias($user, $malias, $mymail);
print "Added alias $malias \n";
}
It expects the desired alias as first argument, the username of the user as second and the email of the user as third argument.
regards
Lukas