DNS paranoia

[Simon Rae]

I'm having a few problems with qmail (1.03 on Linux) returning 5.1.2
errors for mail destined to various sites. This just happens
occasionally for hosts/domains which definitely do exist. I'm suspecting
it could be due to DNS timeouts while querying our DNS servers due to
line traffic. Does this sound feasible? Is there anything I can do to
remedy this apart from splash out extra cash on a line upgrade (assuming
this is the problem)?

Ta

Simon