Postfix alias entire domain (*.newdomain.tld -> *.olddomain.tld)

I have a customer who has around 100 mailboxs + all the aliases. He has now purchased a new domain name and requires all email address in the new domain to be sent to the old domain which will remain the master. Alias *.newdomain.tld -> *.olddomain.tld.
At the moment the only way I can see to do this would be to create an alias for each mailbox and aliases in the old domain

 

I found this on the internet, where would be the safest place to put it in the Ispconfig 3 files. is it safe to just edit the /etc/postfix/virtual file.?
"You can do this by inserting a @domain.from: @domain.to line into your virtual aliased map, which is in most cases in /etc/postfix/virtual. After that, you shouldn't forget to rerun a postmap virtual command to recreate its database!"

 

if you use ispconfig 3, you should use the domain alias feature in email section

 

Thank you. The most obvious things are always right under your nose. Read the manual and for some reason skipped that entry.