Duplicate e-mails getting sent through SMTP

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Joined: Tue Jun 23, 2009 8:24 pm

Duplicate e-mails getting sent through SMTP

Postby Wowbagger » Wed Jun 24, 2009 3:39 pm

I have a custom-built application that seems to be delivering duplicate e-mails. I do not think my own logic is at fault. I managed to trace the problem to the SMTP system: "Send" would get called once, and two (or, rarely, more) would actually get sent out.

I did some homework, and discovered a few resources on this. Some examples:
This old paper: http://www.ietf.org/rfc/rfc1047.txt
This from MailEnable's knowledge base: http://www.mailenable.com/kb/Content/Ar ... D=me020470

However, I still do not think I completely resolved the issue. A few recipients are complaining that they are still getting some duplicates.

Is there any further advice or good resources someone can point me to?

Would it be possible to set up a rule for MailEnable to ignore dupes? ("If the To, From, and Subject are exactly the same, and sent within a second of each other, ignore the second message.")

I have used a few different SMTP APIs, in trying to resolve this.
I have mostly used Microsoft's built-in .NET APIs (System.Web.Mail and System.Net.Mail) and ASPEMail ( http://www.aspemail.com/ ). Plus a few others. But, none of them are any better or worse at it, it seems.

Thanks for any help you can offer!

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Location: Hong Kong

Postby MartynK » Wed Jun 24, 2009 10:15 pm

What is in the various log files can you see the email being processed twice, if so at which point.

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Joined: Tue Jun 23, 2009 8:24 pm

Postby Wowbagger » Fri Jun 26, 2009 3:03 pm

It's difficult to tell, from the logs. We do notice that that there are some requests duplicated immediately after each other, as if the software was sending it out twice in a row. (though, I do believe it is only hitting the .Send command once for each message)

Headers for the dupes received are identical, too.

The problem is very inconsistent, though. It does not always happen.

Also, we send so many messages out, that the whole log is a huge wall to sort through.

(We might open a support ticket with MailEnable, perhaps.)

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Joined: Tue Jun 23, 2009 8:24 pm

Postby Wowbagger » Wed Jul 01, 2009 1:54 pm

Does anyone know if the "maximum number of send threads" setting has anything to do with this?

MailEnable's documentation says the number should be around 7. But, I noticed it was set to 60, on one of our servers.

Could the extra threads be causing a performance issue on the server, that could trigger the SMTP sender to send dupes?

Just a hypothesis.

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Joined: Thu Jul 29, 2004 10:43 am
Location: UK

Re: Duplicate e-mails getting sent through SMTP

Postby johnd34 » Fri May 28, 2010 3:20 pm

I would start by reduing all threads to 1.
Also check that the emails are going to one email account each.
You do nto say how this app is moving the emails into ME

John D
JD Projects

Developer of E-Mailing Systems
West of England
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