Outbound gateway for mail already in spool ?

One of our mail server has been blacklisted by Microsoft mail servers, so I have set up an outbound gateway using another of our mail servers.

It worked fine for new mails but I have been unable to send the mails already in the spool.

I tried reseting tries, forcing delivery, removing files from the spool and adding them again, restarting SmarterMail but to no avail.