This is normally not a huge issue. You are however not mentioning any details on domain structure nor specific volumes.
Given you are sending e.g. 100.000 emails per week on your old PD, and want to shift 10-20.000 of these to the new PD, you should be fine. If you want to start sending 500.000 emails per week on the new PD, you might want to do a ramp-up over few weeks (3-4).
Other aspect, which not many are aware of, is the relationship between your SAP domain and private domain - in context of DMARC. Let's assume you are sending from email.example.com today:
- SAP domain populates the bounce domain: bounce.email.example.com
- Your new private domain populates the from domain: brand2.com
- DMARC fail because example.com does not equal brand2.com
What would work:
- SAP domain populates the bounce domain: bounce.email.example.com
- Private domain populates the from domain: brand2.example.com
- DMARC pass because in both cases they use the domain example.com
So in the past this was only safe if all domains involved were part of the same domain name - or if you did not implement DMARC on those domains. There is a new feature called multi-bounce domain. When that is enabled, the system will always change the bounce domain setting to be bounce.[from domain] - like this:
- From domain: brand2.com
- Bounce domain auto-set to: bounce.brand2.com
Hence you can use a PD different from your SAP domain. Multi bounce is enabled upon request, by submitting a support case requesting help setting up multi-bounce domain support for your new private domain.