I am building Exchange to coexist with several other IMAP mail systems. A typical employee will have several e-mail accounts on different mail systems, and needs their mail delivered to all those systems. For example, my e-mail address is Gideon@xxxxxxxxxxx, but that e-mail address exists on a Cyrus server, a procmail server, and an Exchange server. An SMTP router captures all mail, checks what mail systems a user belongs to, and sends copies of that mail to all the systems. Since Exchange is not capable of sending mail destined to another mailbox within the same store (or within the same server) to an external computer, I need to find a way to force mail to be delivered to the SMTP router so that the mail is delivered to all the mail systems. I am bound by the fact that the infrastructure is already in place for the other mail systems, so I can't make any radical changes to that. I have to use the SMTP router that copies the mail to all the different mail systems. What is really killing me is that all the other mail systems can easily be configured to send e-mails through the SMTP server, but Exchange can only do this if the e-mail is being delivered to an external address. I'm hoping there is a workaround out there, or a third party application that can intercept the e-mails within the store and force them out to the SMTP router. Both MIME Sweeper and Mail Intercept claim to have this functionality, but they only work in very small environments. I need this to work for about 5000 mailboxes (and growing).