>===== Original Message From LISTSERV list owners' forum
<[log in to unmask]> =====
>One of our subscribers just got the following message from our listserv.
>>Your message  is being returned to  you unprocessed because it  appears to
                             <snip>
>>the list recently, either by you or by  someone else...
>
>The subscriber doesn't understand why he got this message, since he only
>submitted it once, and it was approved and distributed.
>
>So, assuming the subscriber didn't actually send a duplicate, what kinds
>of things can cause this condition?
-------------------------------------------
1. They may be using a mail program that will automatically queue mail and
they have tried to send it once... it hasnt gone (generally a message to this
effect displays on the screen citing TCP/IP problems or winsock problems)and
they have tried to send it again, queueing two of exactly the same message.
This also happens with bounced mail, they dont read the message properly and
dont see that the mail is queued on the mail server which will attempt to send
it again later, so they resend the bounce message, ending up queuing two of
the same message again.
(A check on the mail servers logs will show if the message went twice or once
from the originating source. Twice means the above error, once means either of
the next two errors.)

2. There is a time out between his PC and the mail server he is sending
through, the delay does not allow for receipt of the "." end of message line
before the connection is dropped. The mailer does not receive the
acknowledgement of closure, the mail server does record sending the
acknowledgement and sends the mail, the PC side mail software assumes it isnt
sent and sends it again. (Usually in a system such as gatewayed mail software
where there is a controlling body between the PC and the mail server).

3. There is a broken pipe between your subscriber and you, causing a second
distribution of the same mail message because of the non-receipt of end of
message acknowledgement. A 'not worth the effort' tracing, generally
non-repeating error that will stop. Longest I have heard of a broken pipe
causing problems of this sort is 3 days (long weekend). Most seem to pick it
up by then and fix it on the 4th day.

Broken pipes are the most likely cause with automatic mail software being
given the same message twice being the next most likely. Neither are in your
control as a list owner unless you access the mail server with root or
administrator privileges (or equivalent). Your sender could ask their admins
about time-out values for SMTP connections on their mail server and their
individual software components of their mail system and get them to raise the
lowest or governing one if the problem persists. Otherwise, you both just have
to put up with it until it goes away.

ICoS

NOTE: Unless someone actually fiddles their headers so that the
default-reply-to address and the from address is specified as your original
sender, so the original sender gets the bounce from the second message, then
it is not a message sent again from a separate list subscriber. (Headers
should help with this one, depends on whether you know what to look for to see
if a header is faked in any part of it, although why someone would bother just
to send a bounce back to a specified person is beyond me)

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