I’m sure this is documented somewhere, but apparently I’m an idiot and don’t understand the description of what NextCloud actually is. I was reading the NextCloud website and it has something called Groupware. It mentions email. After installing NextCloud on a linode instance, I can’t seem to find where one would setup email.
So, that begs the question, does NextCloud Groupware include a mail server? If so, how does one go about configuring it?
It does not contain a mailserver. Nextcloud uses an existing mailserver using IMAP, SMTP, CalDAV, CardDAV. So the Nextcloud apps “Mail” and “Calendar” may be used then.
Thank you for the response! I figured that was the case, but wanted to hold out hope that it was a “all-in-one” solution. Any suggestions on an open-source mail server I can plop on the same machine?
I don’t know, whether it will work with a currently installed server, maybe mailcow as a docker instance might work: https://mailcow.email
sendmail and dovecot on the local system.
I wouldn’t recommend doing that.
Mailcow is great. But I’d recommend running it on a separte box / VM. However they offer an (unsupported) script, in order to install Nextcloud on an existing Mailcow instance, But I’m not a big fan of that either. I would keep these things separate. It’s easier to mainatin and also better from a security standpoint.
I would recommend that even less, unless you know exactley what you’re doing. 
To be precise, Nextcloud Mail requires an external IMAP/SMTP mail server, but it is it’s own CalDAV & CardDAV server.
Thank you all for the fantastic information and suggestions. I will look into creating a second VM and test out MailCow
On the other hand: Your Linux is able to manage an own mailsever with postfix and dovecot. Just install the packages and configure them. Nextcloud should be able to handle the account(s).
So you will not need an additional groupware.