Mailer fails with bind8

[s.g.kamath at usa.net]

I have a problem with KX mailer and bind8.   When the KX mailer sends a
mail to domain say xxx.yyy, it fails.
Looking at the trace,   I see the following :
1.  The mailer sends an MX query to the name server for the query name
xxx.yyy
2.  The name server sends a response  with SOA records, but no MX
records.
3.   The mailer now sends an A query to the name server  with the query
name xxx.yyy.   This is as per RFC 974 - that when a mailer receives no
MX records, it is supposed to treat it as  if it contained one RR, an MX
RR with a preference value of 0, and host name name of xxx.yyy
4.  The name server responds back with the A records.

However, the mailer still fails.   Has anyone come across this
problem?   Isn't it a problem with the mailer?  Could anyone advise  on
this?    Is there any RFC that suggests what the mailer is supposed to
do?

Thanks