I have a G Suite account for, let's say, domain.com. I have a user with email address me@domain.com. Today I added a new domain to the account new-domain.com and set up an email alias for my user, which is me@new-domain.com.
Since "New Domain" is my new company name, I want to transition to the new email address and eventually get rid of the old one. To help avoid confusion during this transition, I want anyone who emails the old address (me@domain.com) to get an auto-response like "Please use my new email address in the future...".
What I've Tried
The most obvious thing would be to setup a Vacation Responder, but Gmail doesn't let you specify which address it's for. So there's no way for me to easily specify that responses should only be going to senders emailing me@domain.com. G Suite does have an advanced setting in Gmail where you can quarantine messages. I've tried to use that to quarantine Vacation Responders coming from the new address, but that's not working either because the new address is now the default one, and thus emails coming in to me@domain.com get a Vacation Responder from me@new-domain.com.
To me, this seems like a pretty common situation - transitioning users from one domain to another - and using an alias so users can just have one inbox to check. Does anyone know how to get this to work, or is there some other best practice I could be following?