Multisite & own-domain Emails, WPMS

Hello everyone, this is my first post on here and i'm hoping for some help. I'm currently switching my clients over to a multisite but i want them to retain their cpanel emails. Each client has an account on my WHMCP from which they have their emails and domains configured. From searching the forums, i've figured that i need to update the A record to point the domain to the correct site, however, when i log in to my registrar (123-reg) i have 2 different A records, do i update both of them to point to the multisite?