First open the Mail preferences by clicking on “Mail” in the upper left corner (by the Apple Menu) and then select “Preferences”.
Next you will need to choose the account you want to edit from the list on the left (you may only have one and it will be selected by default).
- Click on the “Accounts” icon at the top of the window.
- Choose the “Account Information” tab.
- At the bottom of this window will be the “Outgoing Mail Server” drop down menu.
Click on the drop down menu and select “Edit SMTP Server List…”
At the top of this window will be the available outgoing mail servers.
- Note that there may only be one server listed. Make sure to select the correct one for the account you wish to edit if there are multiple.
- Change the radio button at the bottom so that “Use Custom Port” is selected.
- Enter the port number that your ISP has suggested for use.
- Make any other changes recommended by your service provider for use with the custom port.
Click “Save Changes” if prompted when closing the Preferences window or when selecting another account to make changes to.