server can't be both mail and dns slave
I setup a multi-server setup with 2 servers, one web/mysql/dns and the second mail/dns. This seems to be an unsupported combination, as you must configure the second server as a slave of the first in order for DNS to work correctly, and you must configure it to not be a slave for email to work correctly.
Problem symptoms: when configured as a slave, you can't select this server when you try to add a new email domain/address/etc. - when not configured as a slave, you don't get dns zones setup on both dns servers, only one or the other (whichever you select in the menu).
I tried making the first server a slave of the second, and a similar problem exists in mysql, ie. you cannot select the first server from the list when you add a database.