Hi all, hope someone can help with this. We are an ISP running a POP3 and an IMAP server, both running Debian 5.0.3. One of our domains 'somewhere.com' has several email accounts, some of them POP3 and some of them IMAP. email@example.com (imap.server.com) firstname.lastname@example.org (pop3.server.com) Squirrelmail is installed on the IMAP server, and when 'email@example.com' (IMAP) tries to send an email to 'firstname.lastname@example.org' (POP3) they get the following error: "Requested action not taken: mailbox unavailable Server replied: 550 5.1.1 <email@example.com>: Recipient address rejected: User unknown in virtual mailbox table" Now, this would be happening as the 'office@' user is on the POP3 server which is external. But as there are other email accounts for 'somewhere.com' on this IMAP server, it is looking for that in the mailbox table and seeing that it doesn't exist, hence throwing up the above error. I have tried to force squirrelmail/postfix to use an external relay server but it still appears to be sending through local host. I have edited relayhost in main.cf and Squirrelmail config.php but to no avail. It still doesn't seem to be working. Can someone please help with this? Please let me know if you need any more info. Thanks!