setting up mail hosting and MX modification (bluehost)

setting up mail hosting and MX modification (bluehost)

Though the Zoho instructions are pretty clear, I am not sure of all these steps.

I am setting up mail hosting thru zoho at my domain hosted by bluehost (CPanel). I already have several email forwards using the domain.

I'm confused because in the Email options in Cpanel, I can find the MX Entry but the explanation says "An MX (mail exchanger) entry tells a client which server receives mail sent to a domain name."

I'm not clear what happens with MX modification. Is that going to change ALL the email accounts/forwarders I have at this domain to Zoho? Or just the user accounts I set up? I was hoping for the latter but don't see in Cpanel @ bluehost where this will happen.