When setting up your Mailbox email account on your Apple computer's MacMail program, follow the steps below:
Click on your Mail program and click on Add Account...
From there, will be prompted to Choose a Mail account provider... Choose Other Mail Account... then click on Continue.
On the Add a Mail account window, enter your name, email address, and password, then click on Sign In.
The final step is to enter the Account Type along with the Incoming Mail Server and the Outgoing Mail Server, which are both secure.emailsrvr.com.
Click on Next and the set up will complete itself!