Open Apple Mail.

If you are not prompted to create an account, go to Mail -> Preferences.

Click on the + button in the lower left hand corner.

Type in your name as you want it to appear on outgoing emails.
Type in your email address and password.
Click Continue.

Type in the incoming mail server information.
Account Type: IMAP
Description: imap.(your domain name)
Incoming Mail Server: imap.(your domain name)
User Name: Your Complete Email Address
Password: Your Password
Click Continue.

Type in the outgoing mail server information.
Description: smtp.(your domain name)
Outgoing Mail Server: smtp.(your domain name)
Make sure User only this server is checked on.
Check on "Use Authentication"
Type in your complete email for the username and password.
Click Continue.

Uncheck "Use Secure Sockets Layer (SSL)".
Keep authentication at Password.
Click Continue.

Click on Create.

On the Accounts page, click on smtp.(your domain name) next to "Outgoing Mail Server (SMTP)" and go to Edit Server List...

Click on "Use custom port:" and put in 2500. Be sure that "Use Secure Sockets Layer (SSL)" is still unchecked and that your username and password are entered in.
Click OK.

Go to the Advanced tab along the top.
Change the option of "Keep copies of messages for offline viewing" to "Only messages I've read."
Ensure that the Port listed there is 143 and not 993 and Use SSL is not checked.

Click on the red button in the upper left hand corner to shut the window (being sure to click Save when it asks you) and go to your mailbox.
On the left hand side, you should see IMAP.(your domain name) with an arrow next to it.
Click on that arrow and you should see all of your folders.

Click on your Sent Items folder.
Go to Mailbox -> Use This Mailbox For -> Sent.

Do the same for the Drafts and Deleted Items (Trash) folders.

Your setup is complete!