Can AppleScript/Mail recover from non-existent email address?

Question

I have an AppleScript which automatically sends HTML emails after a delay of a few days from receipt of an incoming email produced by a web form. It works well except for one issue:
The address it sends to are picked up from the web form so I have been testing failure modes for various badly formed email addresses. Most fail gracefully with NDNs except if the domain does not exist. In this case Mail opens a dialog window with "Cannot send message using server etc". This is not good for an unattended Mac automatically processing thousands of emails a day. Mail appears not to inform AppleScript of this glitch.
Any thoughts about a solution would be appreciated.
I only have Tiger and Leopard but this script will eventually run on a recent Mac.

Answer 1

This is a style thing, but I try to write my code so it is easy to debug.
if (do shell script "x='" & w & "';
z=${x##*@};
t=`dig +short ${z%>*} MX`;
echo ${#t}") > 0 then display dialog "send"
It is hard to debug what is being passed to Unix.
I'd write this something like
[[ I have not tested this ! ]]
[ I have not taken in Hiroto's comments ]:
-- I write the code so as to debug it.  I would not assume the statement above would work the first time.
-- I let the log statements in the final code.  They do not do anything outside of the script editor.
set toUnix to  "x='" & w & "';
z=${x##*@};
t=`dig +short ${z%>*} MX`;
echo ${#t}"
log "toUnix = " & toUnix
set result to do shell toUnix
log "result = " & result
-- I do not understand this statement. Shoudn't we be testing for the length of result? Or not equal to null?
if result > 0 then
  display dialog "send"