Goto Add Account.. option from Mail Menu of apple Mail.
Step 1 : Select Add Account
Select Add Other Mail Account… then click on Continue
Step 2 : Select Add Other Mail Account
Add a Mail Account details: Name, Email and Password then click Create
Step 3 : Add a Mail Account details
Add Incoming Mail Server Info : Select IMAP in account type, then Enter your IMAP Mail Server address, Your full email address as User Name and password then click Next
Step 4 : Add Incoming Mail Server Info
Verify Certificate : If you have configure SSL on your imap and if it is self signed certificate then you might get this additional box, Just click Connect.
Step 5 : Verify Certificate
Outgoing Mail server Info : Just Enter your SMTP mail server details then click Create