Good day to all the Fundi's, Gurus and other knowlegable & clever people,

I installed ZCS 8.0.4 on SLES11 and uses fetcmail to collect external mail from a drop box. (Thanks again, Vavai!)
MTA relays via the ISP.

I can send and receive inernally.
I receive external mail.
Sending external mail gets returned with:
Reporting-MTA: dns; arkmail.arktrading.com.na
X-Postfix-Queue-ID: 1B5A01BC30A
X-Postfix-Sender: rfc822; test@arktrading.com.na
Arrival-Date: Tue, 25 Jun 2013 10:50:56 +0100 (WAT)

Final-Recipient: rfc822; stefaug@iway.na
Original-Recipient: rfc822;stefaug@iway.na
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; iway.na
The DNS records:
Code:
zimbra@arkmail:~> zmcontrol -v
Release 8.0.4_GA_5737.SLES11_64_20130524120036 SLES11_64 FOSS edition.

zimbra@arkmail:~> dig arktrading.com.na mx

; <<>> DiG 9.6-ESV-R5-P1 <<>> arktrading.com.na mx
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 41906
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 2

;; QUESTION SECTION:
;arktrading.com.na.             IN      MX

;; ANSWER SECTION:
arktrading.com.na.      172800  IN      MX      10 arkmail.arktrading.com.na.

;; AUTHORITY SECTION:
arktrading.com.na.      172800  IN      NS      ns1.arktrading.com.na.

;; ADDITIONAL SECTION:
arkmail.arktrading.com.na. 172800 IN    A       192.168.10.251
ns1.arktrading.com.na.  172800  IN      A       192.168.10.251

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Jun 25 11:03:21 2013
;; MSG SIZE  rcvd: 109

zimbra@arkmail:~> nslookup ns1.arktrading.com.na
Server:         127.0.0.1
Address:        127.0.0.1#53

Name:   ns1.arktrading.com.na
Address: 192.168.10.251

zimbra@arkmail:~> nslookup arkmail.arktrading.com.na
Server:         127.0.0.1
Address:        127.0.0.1#53

Name:   arkmail.arktrading.com.na
Address: 192.168.10.251

zimbra@arkmail:~> cat /var/lib/named/master/arktrading.com.na
$TTL 2D
@               IN SOA          arkmail.arktrading.com.na.      root.arkmail.arktrading.com.na. (
                                2013061701      ; serial
                                3H              ; refresh
                                1H              ; retry
                                1W              ; expiry
                                1D )            ; minimum

arktrading.com.na.      IN MX           10 arkmail.arktrading.com.na.
arktrading.com.na.      IN NS           ns1.arktrading.com.na.
ns1             IN A            192.168.10.251
arkmail         IN A            192.168.10.251
zimbra@arkmail:~>
I perused all 10 pages on searching for X-Postfix - could not find a solution.
I installed the password security for the ISP SMTP server as per the WIKI - no avail.
I tested if port 25 is open to the ISP:
Code:
zimbra@arkmail:~> nslookup
> iway.na
Server:         127.0.0.1
Address:        127.0.0.1#53

Non-authoritative answer:
Name:   iway.na
Address: 196.44.136.22
>
zimbra@arkmail:~> logout
arkmail:~ # nslookup
> iway.na
Server:         127.0.0.1
Address:        127.0.0.1#53

Non-authoritative answer:
Name:   iway.na
Address: 196.44.136.22
>
arkmail:~ # su - zimbra
zimbra@arkmail:~> telnet smtp.iway.na 25
Trying 196.44.136.51...
Connected to smtp.iway.na.
Escape character is '^]'.
220 mx2.iway.na NO UCE ESMTP Status=Connected
^]
telnet> quit
Connection closed.
zimbra@arkmail:~>
I cannot find anything significant in the logs.

Please help.