I have set the "search mydomain.com" in resolv.conf, but any host that can't be found defaults to a host in my own domain.

For example, if I'm looking for antihost.yourdomain.com (which doesn't have an IP from your DNS server), my local box will eventually try to lookup antihost.mydomain.com.

Only this lookup will result in the default server for my domain (I have a wildcard for any "<host>.mydomain.com" forward to "server1.mydomain.com" to avoid excessive host aliases.

Is there any way to prevent the antihost.yourdomain.com from resolving to antihost.mydomain.com (as by default antihost.mydomain.com will result in the IP for server1.mydomain.com)?

While I could just manually add CNAME records for only the hosts I want, I'd prefer not to do this.

Many thanks,

Ives

My understanding of DNS does not support what you are saying. However, it is very possible that what is being looked for is actually:
antihost.yourdomain.com.mydomain.com

Is there a way to prevent this? I'm not sure, but I would check your DNS files to make sure that "mydomain.com." is properly terminated with root (.) at the ends (where appropriate).