Are we able to use same IP address in more than one Marketo instance?
Do you mean can 2 different Marketo instances have the same dedicated IP? That would contradict the notion of “dedicated.”
What exactly are you trying to accomplish?
Client has purchased new dedicated IP for a new Marketo instance.
Question:
Are we able to have same email sender in more than 1 Marketo instance? By configuring SPF/DKIM?
Let's say, marketo.com in more than 1 Marketo instance?
Are we able to have same email sender in more than 1 Marketo instance?
Of course. You use different DKIM selectors and different branded envelope domains. (Note the SPF record only matters for your envelope domain, the From: domain’s SPF record is not checked.)