What is needed for email automation?
The subject line isn't long enough, so I will clarify here.
I'm wondering what is necessary at a minimam on a Linode system (regardless of distribution) to have applications like WordPress, etc send out automated emails?
Many applications can be configured to use an external SMTP server to send mails.
Yep, though I still like to point such applications at localhost (with a local MTA like postfix/exim/etc…) since then I have local queuing/retrying if there's a network problem, as well as central logs of what has transpired with mail. Not all applications will implement those features when pointed directly at an external server. You also eliminate any possibility of delay to the application while talking to a remote server.
You can still point the local MTA at the same external SMTP server that you would have given an application, but it gives you a separate control point outside of your applications, plus a single spot for any configuration for that external server, if you have multiple applications.
With most distributions the overhead to install a send-only MTA is pretty small. And odds favor you'll want it anyway for something else, even if only mail from daemons like cron.