This article will explain how to setup Apple Mail with POP3 or IMAP
Open Mail and go to Preferences.
Click on to the accounts tab and click on the '+' on the bottom left to add a new account.
You will then be asked to select the type of account you are adding to the application. Click on the Add Other Mail Account option and click the Continue button.
Next you have to add some account information: your name, your mailbox email address and its associated password, in the boxes provided. Once complete, click the Create button.
You will receive a notice saying that your "Account must be manually configured". If you receive this, click the Next button.
Next you will be asked to add your incoming mail server information. Here you can select whether you would like us the POP3 Protocol, or the IMAP protocol. The POP protocol means that your email will be downloaded from the server it is stored on, and stored locally to wherever you access it. IMAP will allow you to read and manage your mail directly from the server view your client or device, and even allows you to use multiple devices, including mobile devices.
Next you will need to configure your Outgoing Mail Server information. This will be the same for both the IMAP protocol and the POP3 protocol.
The SMTP server details will be smtp.123-reg.co.uk, and the username will be your email address, and the password will be the password associated with the account. Once entered, click the Create button.
You may get a notification that additional account information is required. In this case, click the Next button.
Keep the port as 587, and again, the Authentication setting as Password, then click the Create button.
This completes the process. Your account will now be synced with Mac Mail.