Reset Apple Mail 12.4 SMTP Server Settings List?

I have searched for an answer to this a number of times for a number of different, recent versions of Apple Mail without success. Hopefully one of the wizards on TidBITS has the answer.

When navigating here:

Apple Mail/Preferences/Accounts/anyaccount/Server Settings/Outgoing Mail Account:/drop down menu

I have a long list of outdated, unused or otherwise incorrect, smtp server entries. My goal is to clear that list to the default of zero entries. I was optimistic a plist might contain that information but if there is one I have been unable to locate it.

I am repeatedly experiencing outgoing smtp errors and believe this step may well be the solution to resolving it.