@kalder said in Opera mail client duplicates sent messages:
I am still puzzled about why only Opera (my 12.x version, Opera Mail and standalone) duplicate sent messages, whereas Outlook and smartphone app do not. And why all this started a few weeks ago...
Maybe something changed on the server where the server is no longer ignoring Opera's duplicate and it still ignores other clients' duplicates. And or, maybe some other clients don't add a copy of the sent message if it's an exchange server. I'm not sure. I would guess that for Outlook, it's probably not using IMAP to connect and is using the actual exchange protocols etc. For the smartphone app, I guess maybe look in the settings. It may reveal something.
I'm pretty sure Exchange has been creating its own sent copies for a while, so I doubt that was off and hotmail all of sudden turned it on.