In the MDaemon UI, Setup -> Server Settings -> DNS & IPs -> DNS -> Edit MX cache file can be used to override where MDaemon delivers an email to an external domain. Instead of using the results returned by the DNS server, it will instead act on the value in the MX cache.
This can be useful if you can’t deliver and email to a domain directly, but it does work if it’s sent via your ISP.
The MX cache file looks like this:
For example, to send mail addressed to aol.com through isp.smarthost.mail, the entry would be:
aol.com 10 isp.smarthost.mail
If you need to enter a username and password before isp.smarthost.mail will accept the email for onward delivery you may do so:
aol.com 10 isp.smarthost.mail email@example.com password