Mail not forwarding to Zimbra Collaboration 8.6 - also DNS Problem Email Address appears to be wrong

Hello, Email is not hitting Zimbra from ispconfig 3 but I am not getting any errors bounced back.

Should the relay recipient be server.domain.com subdomain.domain.com or should the mailbox be included:[email protected]?

Should both the domain and the destination have full stops at the end in Email Routing or in Relay Recipients?

The other thing that the IRC DNS forum picked up was that the Email address for DNS problems appears to be wrong - it has a period in the wrong place apparently but I also read that the system sometimes does this - i'm not quite sure how to rectify it - that's if it is actually an issue - I did the same check in duckduckgo search engine typing whois and the Email address seemed fine but I presume there is a separate Email address for this from within the ISPConfig 3 panel

What I currently have or what I am at least trying to have:

1) I have one static external IP.
2) I have one internal server that runs ISPConfig 3
3) I have one internal server that runs Zimbra Collaboration 8.6
4) I am looking to have mail for subdomains of my choice go to my zimbra install via either an internal IP for an FQDN (Please could you tell me whether both or one of these would be correct please?)

My Configuration:

Thank you and credits to 'till' for pointing me in the right direction about this bit:

A) I have Email routing set up - domain is currently set to subdomain.domain.com. (with a full stop) within this section of the panel (where this has been blanked by me for public post) and the destination as mailserver.domain.com. (with a full stop at the end) and ticked as active;

B) I have Relay Recipients set up - Relay Recipient it set to subdomain.domain.com (with a full stop at the end);

Thank you so much for your time - i've been pulling my hair out trying to get these issues sorted over the last couple of weeks - it would be so nice to get things working properly

Kind Regards,

indieben.

 

Thanks Till:
The reason I tried the full stops (and I am back at this now) was because I am getting this Email:

"This is the mail system at host host.domain.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<[email protected]>: mail for mail.domain.com
loops back to myself"

Thanks for your time