OE strange problem!!! Need Expert help!!!

I am using OE6 and my SMTP is provided by my ISP's Linux Server. And my mail
file is really big (~8GB in many sub mail folder).

Sometime when I send a email to A@A.com, and finally A@A.com & B@B.com will
also got the mail. I didn't do any cc or bcc!

However, In my mail outbox, I read the source of that mail, the recipient is
only "A <A@A.com>".

Also, I check with the person A & B, and what they got is the same! In the
mail header there are only "A <A@A.com>" as recipient!

And the mail to A & B got the same Message ID.

I check with my ISP and got the SMTP log from them (we use the Message ID to
search it out). The log really show me that I did post the mail to A & B.

After that I changed to use another ISP's SMTP server, but the same problem
happen.

I also checked my address book, the name and address is correct. And no any
"A <b@b.com>" incorrect address.

My dear expert, it is any realted to wrong index of my address book, so that
sometime it will send to wrong person and some time didn't?

As sometime, when I search out some message, and once I click on that
message it will show me another different message!!

Please, give me some hints!!

Many thanks!

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May