There is no requirement that your AD domain be an Exchange SMTP domain. If you want Autodiscover to work, you will need an autodiscover.domain2.com DNS entry and the server to answer it because it's derived from the SMTP address. Everything else
can go through whatever hostname you want, but remember that all the domains you use has to be in your certificate.
Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."