I found out a problem with mx preferences on GWIA.

One of recipient's domain has 2 records. They look like:

RecipientDomain.com MX preference = 10, mail exchanger = TrueServer.An-Antispam-Company.com
RecipientDomain.com MX preference = 20, mail exchanger = HoneyPot.An-Antispam-Company.com
The server HoneyPot.An-Antispam-Company.com - always says "421 Service Temporarily Unavailable".
This is permanent answer.

Only TrueServer.An-Antispam-Company.com - can receive emails.

This is part of their antispam solution I think. Something like nolisting (Nolisting - Wikipedia, the free encyclopedia)

When WGIA do nslookup there are two possible answers:
1.
RecipientDomain.com MX preference = 10, mail exchanger = TrueServer.An-Antispam-Company.com
RecipientDomain.com MX preference = 20, mail exchanger = HoneyPot.An-Antispam-Company.com
2.
RecipientDomain.com MX preference = 20, mail exchanger = HoneyPot.An-Antispam-Company.com
RecipientDomain.com MX preference = 10, mail exchanger = TrueServer.An-Antispam-Company.com
Both answers are equal but records in different order. The problem is that GWIA ignore "preference = xx" field or it could not choose random server. GWIA always chose the first server from answer.

In first case GWIA will send email to TrueServer.An-Antispam-Company.com - there is not any problem.

In second case GWIA will send email only to HoneyPot.An-Antispam-Company.com again and again and again. And each time answer will be "421 Service Temporarily Unavailable".

After ttl time - DNS Server could change sequence. ttl of RecipientDomain.com is 6 hours, so in result the user should wait 6 hours and _IF_ (50/50) the order will be changed the message will be delivered.

Is it a GWIA problem/bug (to chose only /and always/ a first record and ignore the preference)?
Is there any DNS lookup settings in GWIA?

Or it is the DNS server problem?

PS.
GW 8.0.1HP1 on Netware 6.5 SP6,
DNS server - Windows 2000 Server SP4