The other copy is the one that Opera appends to the IMAP "sent" folder. This is what Opera is supposed to do. Unfortunately, Opera doesn't have an IMAP "don't place copy of message in sent" folder option to work around servers that create the copy themselves.

Now, you can unset the sent folder on the IMAP tab in the account's properties. But, then Opera will no longer treat messages in that IMAP sent folder as sent. Further, in the case of exhange IMAP, Opera doesn't let you keep the sent folder unset. It'll get set again. I even tried closing down Opera and editing incomingN.txt for the account to disable special use (server doesn't seem to be using it) so the sent folder isn't forced. But, that doesn't help. And, even if you can blank out the sent folder setting for a bit, it gets turned back to "sent" all the while still placing a copy on the server.

Long story short, you can't avoid the having 2 copies with Opera mail. You can't even hide them by unchecking "show duplicates" because they're not true duplicates. The copy the server creates has a whole bunch of ms-exchange headers in it. All you can do is hide the server-created copy with a label set to "hide these messages from other views" (with "apply only to new" unchecked) set, with "show hidden" unchecked for your sent views with the following rules for the label:

From header contains you@example.com
and
any header contains x-ms-exchange

There is a does not contain rule where you can try to hide Opera's copies instead. You'll have to play with that.

That's about it.

If i set the sent items in white, i get the same result.

If you set it to white (as in, no sent folder set), close out of the mail account properties to save the change and then restart Opera, does it stay white or does it revert back to "Sent items" on you?

I was thinking that the Hotmail SMTP server adds a copy of the sent message to "Sent Items" itself and when you have "Sent Items" set as the IMAP sent folder, Opera adds a copy also. If that's the case though, then not setting an IMAP sent folder in Opera should get rid of the one copy (you won't be able to control the copy the SMTP server generates). However, you said blanking out the IMAP sent folder setting in Opera doesn't help, so that's probably not the issue unless the sent folder is getting set to "Sent Items" again on you.

I'll have to play with my hotmail account more and see what I can find. I don't use it very often.

I use hotmail imap?

On the "outgoing" tab in the account's properties in Opera Mail, do you have "Sent Items" set as the IMAP sent folder?

Are you using Gmail IMAP?

You could try this though. "Menu -> Settings -> Import and export -> Export Contacts". Then, select all contacts in the contacts panel and trash them. Then, empty the trash. Then restart Opera Mail. Then, compose a new message to a person and send it to see if it still sends twice. If not, it's something to do with one of the contacts. When you're all done, you can import your contacts back in.