[Ubuntu] Problems with mail (Postfix/Dovecot)

[Helx]

I've recently decided that I want to setup a mail server myself, oh how difficult that has proven to be so far.
I'm not expecting a reply, because Jacek is the Ubuntu-pro. I may as well try.

I followed this tutorial: https://www.exratione.com/2012/05/a-mai ... cot-mysql/

When trying to send mail to another email from PostfixAdmin (I know, it's probably local-only, but I don't have multiple emails setup to try) I get this error message in my /var/log/mail.log file:

Mar 28 06:16:07 crook postfix/smtpd[16067]: warning: dict_nis_init: NIS domain name not set - NIS lookups disabled
Mar 28 06:16:07 crook postfix/smtpd[16067]: connect from localhost[127.0.0.1]
Mar 28 06:16:07 crook postfix/smtpd[16067]: warning: SASL: Connect to private/auth failed: No such file or directory
Mar 28 06:16:07 crook postfix/smtpd[16067]: fatal: no SASL authentication mechanisms
Mar 28 06:16:08 crook postfix/master[11256]: warning: process /usr/lib/postfix/smtpd pid 16067 exit status 1
Mar 28 06:16:08 crook postfix/master[11256]: warning: /usr/lib/postfix/smtpd: bad command startup -- throttling

And this in my /var/log/mail.err:

Mar 28 06:16:07 crook postfix/smtpd[16067]: fatal: no SASL authentication mechanisms

When I try to login to with RoundCube, I get the following error (on-page, after turning debug on):

IMAP Error in /usr/share/roundcube/program/include/rcube_imap.php (205): Login failed for ***@***.nz from <my IP>. Could not connect to localhost:143: Connection refused

I remember not wanting to deal with SSL certificates, so I tried leaving anything with that out (e.g. when something said "require ssl" to yes [as an example] I would say no).

There are a lot of config files, so I'm not going to post them. Please tell me what files you'd need to see.
I also understand that this could be because of my DNS configuration, but I am also not sure about that either. Again, please let me know.