Exchange Hybrid SSL Certificate Question

Hello,

Would like to ask reg SSL Certificate for Hybrid. I have Exchange 2013.

We have the following domains.

Parent domain - domain1.com (No SMTP, Not using as email address)

Other domains - domain2.com, domain3.com, domain4.com (Used as email address)

Question is, do I need to add domain1.com as part of my SSL Certificate or I just need to use other domains?

TIA!