[exim] Outlook problem

This is rather off topic, but I can't find any information on this problem,
so perhaps someone on this list can help:

When a message being sent by Outlook is rejected at RCPT time, Outlook
carries on sending the message regardless:

Outlook log:

06:10:06 SMTP: [tx] MAIL FROM: <*****>
06:10:06 SMTP: <rx> 250 OK
06:10:06 SMTP: [tx] RCPT TO: <*****>
06:10:06 SMTP: <rx> 550-Verification failed for <*****>
06:10:06 SMTP: <rx> 550-unrouteable mail domain "example.com"
06:10:06 SMTP: <rx> 550 <*****> does not appear to be a valid sender
address.
06:10:06 SMTP: [tx] DATA
06:10:07 SMTP: <rx> 503 valid RCPT command must precede DATA
06:10:07 SMTP: End execution

Outlook then reports the 503 error instead of the 550 error, which means the
end user never gets to see what the problem actually is.

Is there any way of making Outlook give up when it sees the 550 error?