I don't know what you can do. What you have done so far is block legitimate email servers from sending your clients email, while reducing your load, it is not a good practice. If you are going to do something like that you might as well just turn off your mail server.
I totally agree with you and I know that I'm blocking what I don't want to, but if I don't, my server gets so busy that nobody can send messages cause it's a small machine to handle only two domains, one with 2 and other with 154 accounts, and I only have some load on a business hours.
Is this server delivering mail and are you checking for unknown users at smtp time (via the chkuser patch)?
Yes. It's all fine. So I think thats the only thing to do is wait...
Thanks everybody for your time.
Regards, -- Walter.