Email uses a minimum of two servers; one for receiving (POP or IMAP) and the other for sending (SMTP).
Typically when you set up an email account in the Mail app, the app tries to configure the proper servers based on the email address you provide it. This works well for the most common email providers out there. However, if you run a private email server or use a lesser know email provider, it may require you to enter the proper server information manually.
You would do so, via the Mail app, as follows:
- From the Mail menu bar, select Mail > Preferences > Accounts
- Click on the "+" button at the bottom of the left window to add a new email account.
- Either select one of the pre-existing accounts or choose "Other Mail Account..." Most likely, this will be the one you will want to pick.
- Select it, and then, click on Continue.
- Enter the desired name in the Name field.
- Enter the email address and account password in the next two fields.
- BEFORE clicking on Sign In, hold down the Option key, and then, click on Sign In.
- You will now have the opportunity to enter both the account type and the incoming and outgoing mail servers.