Hi, While I don't have hundreds of domains using ip mapping I do have thousands of users mapped to 3 different individual domains. That is a left over from our move from sendmail to qmail and merging all the old mail servers into one. All the new client domains are setup to use full user @ domain, but it's not really an option for the 3 main domains (Our original ISP, plus 2 other ISP's that we bought out).
It's not really an option not to use ip mapping. Regards, Rick