We need help on an issue of sending out duplicate emails.

We use “CDONTS’ to send mail out in an ASP web application and we use MS
Outlook 2003 as well. Sometime it sends duplicate mails. When it happens, the
two duplicated mails are sent very close, within 0.5 second. It does not
depend on the email addresses of both sender and receiver, sometime it gets
better and others it gets worse. We do not know when it started as we phased
in the deployment of the code.

The troubleshooting we have done for it are:

1. Checked the asp code.
I have looked into the code and tried my best to find any possible loop or
any logical problems that may confuse the system, but I did not have any
luck. Also I had set a counter -- it would increase by one if it sent
duplicate mails. But the counter has never been increased when the duplicated
mails happen. I had checked if the system pulled out duplicate email
addresses from the database table as well. It showed me that it did not…

2. We use ADC instead of CDONTS, it did not stopped the duplicate emails.

3. Checked MS Exchange (We have MS Exchange 2000, service pack1)
Our Network engineer checked MS Exchange, but He did not find any problem.

4. Checked SMTP ( We use IIS 5.0 version 1.0)
Our system admin checked SMTP as well. But we did not have any luck either.

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As CDONTS is heavily deprecated, using CDOSYS is a better way to get
support for your config.

CDOSYS will also allow you to send mails through any remote server
(including the "remote" IIS SMTP server on the same box), so that when
troubleshooting issues like this, you can localize the problem to the
client code or the zero-hop server that relays the message. You
would, for example, be able to get very useful information from the
SMTP logs regarding duplicate incoming connections, which is not
relevant using CDONTS.

Sorry I can't be of more direct help, but you seem to have been as
diligent as is possible with the very primitive CDONTS command set. If
you expand to the CDOSYS command set and still see the issue, more
useful troubleshooting can be done.