Question how do I enable webmail on a domain with mail switched off?

[Paris Paraskeva]

how do I enable webmail on a domain with mail switched off?

I have mail switched off since the specific domain is my main company's domain where I use MS Exchange for my email and down rely on my server/plesk setup for emails.

Reason I want to enable webmail.mycompany,.com is to advise my clients to use this to login to their email accounts and make sure its secured with an ssl cert instead of them using webmail.domainA.com webmail.domainB.com, webmail.domainC.com

looking forward to any suggestions around this.