First steps in Dovecot; IMAP not working

[Richard]

> Date: Tuesday, October 18, 2016 13:12:39 +0200
> From: Moi <anic297 at mac.com>
>
> Thank you. It worked and I now have several log files to check.
> 
> In the meantime, I've tried once again to send a message to
> "mailtest" from an outside address; this time, I got an error reply:
> 
> This report relates to a message you sent with the following header
> fields:
> 
>   Message-id: <00e201d2290f$67da8c70$378fa550$@mac.com>
>   Date: Tue, 18 Oct 2016 09:15:21 +0200
>   From: Moi
>   To: 'Mail Test' <mailtest at barbu.sytes.net>
>   Subject: Test
> 
> Your message cannot be delivered to the following recipients:
> 
>   Recipient address: mailtest at barbu.sytes.net
>   Reason: Illegal host/domain name found
> <end of reply>
> 
> Yet another area with a problem; at least this is now a valid
> reason for it to not work.
> Is this a misconfiguration of my DNS server?

Assuming that "barbu.sytes.net" is the intended hostname (not
something made up to obscure the real name), there is an MX-record
for that that points to "mail.barbu.sytes.net", but there is no
A-record for the "mail." hostname. There is an A-record for
"mail.sytes.net", in case that is what you were intending, in which
case you'd need to fix the MX on "barbu.sytes.net".