Some people like to have their domain email set up with Google Mail (henceforth referred to as G-Mail) so that it's in the same place as their personal email account, this is possible by following the steps below:
Click the 'Settings' cog in the top right hand corner of Gmail.
This will take you to the setting menus. Select the 'Accounts and Import' category and then 'Add a POP3 mail account you own'.
Enter the account's address under 'Email Address' and click 'Next Step'.
Type your user name in the 'Username' field and enter the password for that account in the password field.
In the 'POP Server' field you should insert mail.yourdomain and the port should remain set to 110. Choose from the remaining settings as you require and confirm your details.
Click 'Add Account' and make sure 'Yes, I want to be able to send mail as ___' is selected. This will let you send mail from Gmail your account's address in the 'From:' line. Click 'Next Step'.
Enter the name you want to appear as the sender when you send mail using the address in Gmail under 'Name:'.
Click 'Next Step' and then 'Send Verification' on the next window and then return to the Gmail inbox.
Open the 'Gmail Confirmation - Send Mail as ___ message' as soon as it arrives (this may take a couple of minutes).
Copy and paste the confirmation code into the Enter and verify the confirmation code form.
You should now be able to access and send mail from your domain's email address through G-Mail.