System.Web.Mail - Multiple address problem

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I posted this 2 weeks ago but the thread has 'dried up' and I have new
information.
We are using system.web.mail with .Net 1.1 (.Net 2.00 version is under
development) and
some of our users are reporting that having multiple names in the 'to' field
for sending emails (using smtpmail) causes the email not to be sent. Email
server software is Exchange SP2, but other users (including our own test
site) use the same email server without any problems.
The excepton reported is the dreaded 'cannot access CDO object...'.
Everything works fine with only one name in the list, but fails with 2 or
more.
I have checked with the user that there's no problem sending to the same
3 addresses from Outlook on the same server.
Another oddity is that an email with the subject
"alarm240413 new (51.35.03) 22.56"
also gives the 'CDO' error, while exactly the same email without the
brackets, i.e.
"alarm240413 new 51.35.03 22.56"
works just fine. The brackets give no problem on other email servers that we
have tested.
Any help appreciated.

[Hans Kesting]

The excepton reported is the dreaded 'cannot access CDO object...'.

Note: an inner exception gives some more info about the actual error.

Hans Kesting