Hello,
schmerold2@??? <schmerold2@???> (So 17 Mai 2009 17:03:59 CEST):
> We are getting duplicate emails. It seems to be the same senders,
> however not every one of their emails duplicate. 5% of mails from
> Charter.net will duplicate, 10% of mails from Cox will duplicate, 100%
> of mails from Interfax.net will duplicate.
>
> Interfax (a mail to fax provider) is the only sender that consistently
> send duplicate emails. When I asked them to fix it, they said:
>
> "it seems that we are having problems sending you the e-mails and then
> getting confirmations from the mail server that it received them - and
> that is causing us to resend the e-mails over and over."
You should check if the other side gets AND acknowledges your final "250
OK". If you do spam/malware tests during the DATA phase, there might be
some delay between receiving the final "." and sending the final "250
OK". According to RFC 2821 (4.5.3) the client should have a timeout of
10 minutes. But it can happen, that the client terminates the connection
(due to some timeout (have seen 15 seconds already!), the server sends
the "250 OK" and doesn't take care, if the client receives it. In this
case the server processes the mail as usual, but the client will
retransmit the message later over and over.
Some tcpdump/wireshark on your receiving interface could help to
investigate it further.
Best regards from Dresden/Germany
Viele Grüße aus Dresden
Heiko Schlittermann
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