How to configure multiple domains for the same site with Google email


I have three domains that point to the same site, and I’m working on moving them to DH.

domain1 was the original and is set up for GApps email

domain2 is just an alias

domain3 is the new “primary” domain

domain2/3 are aliases for domain1 in GApps
domain1/2 are aliases for domain3 for http

I already have domain3 setup for hosting (WP site) on DH. What do I do with the other two, especially domain1, in order to keep the GApps email working?