Newbie Question #2: MX error preventing incoming emails

Newbie Question #2: MX error preventing incoming emails

I am able to send emails, but unable to receive. I am getting the "MX records not pointed to your domain" message and understand this may be the problem. In reading about account setup however, it states that the MX info correction should be made after all user accounts are added. I have invited other users to set up email accounts but they have yet to respond. Does this mean I can't fix the MX problem until they create their accounts? In the same vein does this mean that I can't add new users after the MX issue is corrected? I'm not well versed about how all this works so my apologies...

Thanks.
Mark