It depends on the plan on you have, on some accounts offer unlimited email addresses. The only space limit is the storage space of your account. As long as you do not exceed the storage limit on your account or the email limit you set, you may have has many emails as you'd like. By default cPanel sets up new accounts with 10 MB of space, but this can be adjusted up or down at your discretion using the Mail menu in cPanel. You may even set your emai accounts to "unlimited" so the only space limit is what is allocated to your account.
Please Note
There is a 10 MB limit on sending and receiving attachments.