Continuing the discussion from Introducing new members on community - 16 Nov 15:
Receiving from and sending with gmail should be a easy, but you use gmail imap and smtp in your client.
If demo1 and demo2 are aliasses of demo@companyA.com that is possible with SOGo (I don’t know if it is configured with the NS implementation of SOGo)
I don’t know if multidomain is possible with NS. Maybe the real NS guru’s can answer this.