How to Change Server Settings in Mail on Mac for IMAP and POP ?
Use Server Settings preferences in Mail to change options for an account’s incoming and outgoing (SMTP) mail servers.
To change these preferences in the Mail app on your Mac, choose Mail > Preferences, click Accounts, then click Server Settings.
Note: The settings you see vary depending on your account type.
IMPORTANT : Please note here my email account is matthew@whc.ca and incoming and outgoing mail server is rachel.whc.ca with SSL used and ports mentioned. If you have any confusion please contact us at support@sibername.com.
For IMAP Account :

For POP : –
