Let’s check the settings. First, launch Mail. Go to the Mail menu and select Preferences. Click the Accounts tab in the Preferences window and choose your AOL email account from the left panel. Go to the Account Information tab and check your AOL email address for any errors. To make a correction, select the Email Address drop-down arrow and choose Edit Email Address. Double-click either your full name or email address, edit the information and then select OK.
Now, Go to the Mail menu and select Preferences. Select the Accounts tab and choose the AOL email account you are having problems with from the left panel. Click the Server Settings tab. Confirm that the Outgoing Mail Account drop-down menu is set to the AOL server. If not, select AOL in the drop-down menu.
Let me know if this helps you out!