This is a very odd problem. I have one user (only one!) whose eMails are
sent twice, but only those eMails that are sent from another application
(e.g., File | Send from Word, etc.). If the eMail is sent directly from OE,
only one message goes. The Sent Items folder shows only one message sent.
But the eMail server log shows two messages sent! There is nothing unusual
about this user's environment - we are all using XP SP3, with the same
antivirus application. I enabled the Mail log. Here is the latest
transaction that doubled from that log:

Outlook Express 6.00.2900.3028 (xpsp_sp2_gdr.061107-0012)
SMTP Log started at 06/18/2010 14:22:04
SMTP: 14:22:05 [rx] 220 mail.xxxxx.com
[XMail 1.26 ESMTP Server] service ready; Fri, 18 Jun 2010 14:22:04 -0700
SMTP: 14:22:05 [tx] EHLO 071XXXXX
SMTP: 14:22:05 [rx] 250-mail.xxxxx.com
SMTP: 14:22:05 [rx] 250-VRFY
SMTP: 14:22:05 [rx] 250-ETRN
SMTP: 14:22:05 [rx] 250-8BITMIME
SMTP: 14:22:05 [rx] 250-PIPELINING
SMTP: 14:22:05 [rx] 250-AUTH LOGIN PLAIN CRAM-MD5
SMTP: 14:22:05 [rx] 250 SIZE 11264000
SMTP: 14:22:05 [tx] AUTH LOGIN
SMTP: 14:22:05 [rx] 334 VYNlcn5gaWU6
SMTP: 14:22:05 [tx] Yn13bHVzY2iib2ltZ0BxYW1gYx5ja20=
SMTP: 14:22:05 [rx] 334 UGFzb3cvdnQ7
SMTP: 14:22:05 [tx] Yn13fiM=
SMTP: 14:22:05 [rx] 235 Authentication successful
SMTP: 14:22:05 [tx] MAIL FROM:
SMTP: 14:22:05 [rx] 250 OK
SMTP: 14:22:05 [tx] RCPT TO:
SMTP: 14:22:05 [rx] 250 OK
SMTP: 14:22:05 [tx] DATA
SMTP: 14:22:05 [rx] 354 Start mail input; end with CRLF.CRLF
SMTP: 14:22:05 [rx] 220 mail.xxxxx.com
[XMail 1.26 ESMTP Server] service ready; Fri, 18 Jun 2010 14:22:05 -0700
SMTP: 14:22:05 [tx] EHLO 071XXXXX
SMTP: 14:22:05 [rx] 250-mail.xxxxx.com
SMTP: 14:22:05 [rx] 250-VRFY
SMTP: 14:22:05 [rx] 250-ETRN
SMTP: 14:22:05 [rx] 250-8BITMIME
SMTP: 14:22:05 [rx] 250-PIPELINING
SMTP: 14:22:05 [rx] 250-AUTH LOGIN PLAIN CRAM-MD5
SMTP: 14:22:05 [rx] 250 SIZE 11264000
SMTP: 14:22:05 [tx] AUTH LOGIN
SMTP: 14:22:05 [rx] 334 VYNlcn5gaWU6
SMTP: 14:22:05 [tx] Yn13bHVzY2iib2ltZ0BxYW1gYx5ja20=
SMTP: 14:22:05 [rx] 334 UGFzb3cvdnQ7
SMTP: 14:22:05 [tx] Yn13fiM=
SMTP: 14:22:05 [rx] 235 Authentication successful
SMTP: 14:22:05 [tx] MAIL FROM:
SMTP: 14:22:05 [rx] 250 OK
SMTP: 14:22:05 [tx] RCPT TO:
SMTP: 14:22:05 [rx] 250 OK
SMTP: 14:22:05 [tx] DATA
SMTP: 14:22:05 [rx] 354 Start mail input; end with CRLF.CRLF
SMTP: 14:22:05 [tx]
..
SMTP: 14:22:05 [tx]
..
SMTP: 14:22:05 [rx] 250 OK S1207DC
SMTP: 14:22:05 [tx] QUIT
SMTP: 14:22:05 [rx] 221 [XMail 1.26 ESMTP Server] service closing
transmission channel
SMTP: 14:22:06 [rx] 250 OK S1207DD
SMTP: 14:22:06 [tx] QUIT
SMTP: 14:22:06 [rx] 221 [XMail 1.26 ESMTP Server] service closing
transmission channel




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