Currently I got this to work so far:
I got Google Apps for Work for my company "Contoso" and I have set up a distribution list via Google Groups so that anyone in the company can send an email to
email@example.com and only members of the support group will receive it. All external users will get a bounce if they try to send an email to this list.
I am stuck on the next bit, we got close partnership with people with
@partner2.tld, and wish to open up our techsupport list to them too, but not anyone else on the internet... how do I do that?
Currently there is only one email address for
@partner1.tld, and not many for
@partner2.tld, so if we were to add extra addresses that are allowed to post the the list that might work for a while too.
EDIT: basically we just need techsupport list to reject all emails unless they are from