i have done the setting for all users but i still am having an issue with duplicate emails of some users
is there not a contrib that can look for incoming duplicates and delete them?
Fix the issue, don't hack around it.
Please go back and read what we previously said about providing some proper debug information.
https://forums.koozali.org/index.php/topic,54724.0.htmlAll we know is you have a SME 10.x in server only mode and use
the worst IMAP client of all Outlook of unknown version.
(IIRC Outlook doesn't properly save Outging mails in the IMAP sent folder unless you run a script to copy from the local Sent to the IMAP sent. Is that still the case?)
Are you using IMAP/POP?
Does you mail server send mail directly or via some upstream server?
Have you tried setting up a test account and access it with JUST webmail or Thunderbird? Get Outlook OUT of the equation.
What is the setup of your server - see instructions above for some debugging output.
What do your logs say?
Without any of this information we just can't - it's just guess work which wastes people time.