Hi I'm having difficulty sending email between users on the same domain when the IMAP server is remote. Let's say the domain is example.com I have ISPConfig3 on Debian 7 with roundcube 1.1.3 installed as an individual site at webmail.example.com I set up roundcube on the local ISPConfig3 server as webmail.example.com (DNS set for local sever) and I set the roundcube configuration file to use the IMAP server at mail.example.com (MX record set for remote server). I did not add any mailboxes for this domain in ISPConfig3 because they are on the remote IMAP server. Email is received from remote senders by the remote SMTP server at mail.example.com I have no control of the remote servers. Outbound email from local roundcube users is sent locally so I didn't change any roundcube SMTP settings, I want local outbound email sent from the local server. Everything works fine for both sending and receiving except that I'm seeing this in the mail log when a user at example.com tries to email another user at example.com: to=<email@example.com>, relay=dovecot, delay=0.24, delays=0.13/0/0/0.11, dsn=5.1.1, status=bounced (user unknown) How do I tell the system to look up the MX record for example.com and send the message to the remote SMTP server instead of trying to deliver it to dovecot locally? I would need to do this only for the domain example.com because the ISPCconfig3 server has other domains which do have the mailboxes on the ISPConfig3 server. Thanks for any help.