I was looking for a way to send mail to one domain on an IP, and all other mail on another domain on another IP. The basic exim remote SMTP set up is


remote_smtp:
driver=smtp


To switch the exim ip, the interface=IP.address configuration is used. But I wanted to have email to a particular domain go over another IP address. I came up with

interface = ${if eq {$domain}{REMOTE.DOMAIN.COM} {IP.TO.SEND.FROM}{DEFAULT.IP} }