Outlook is sending duplicated mails

[Growwing]

Hello dear Microsoft Community 

I've got following problem:

With one of our clients there is an issue with Outlook/Mailing 
The mailbox is IMAP
If he sends Mails to someone they'll recieve the sent message, for like 20 times.
the only suspicous thing is, that we can see 3 duplicates of that mail in the 'sent' folder.
but regardless it was recieved alot more than 3 times, either way.

Do you have an idea ?
I already 
updatet Microsoft Windows & Microsoft Office 365
made a new profile 
checked for Add-Ins or antivirus applications
I also looked it up on our firewall
we also checked the log on the mailserver

greetings
and im looking forward to recieve some help from YOU 

[#2]

Did you grow threw all of these steps?

https://www.msoutlook.info/question/multiple-email-copies-being-sent

@Growwing 

[#3]

Hi,

In Outlook : File --> Account Settings --> Double Click the Account Name (highlighted yellow in the screen below) --> More Settings --> Tab Sent Items --> Choose option " Do not save copies of sent items".  Refer to the screen shot below.

This will ensure that Outlook doesn't store an additional copy of email since Gmail already doing the same. So with this you will be still having one email (IMAP) in your outlook/ gmail sent folder .

Thanks,

Deepak

[#4]

@Growwing I think I can understand the pain as I have encountered the same error. This problem makes the inbox very disarranged and unmanageable. Moreover, if you have a business account, then having multiple email copies will affect productivity as well. It took me lots of crucial hours because of this as I was supposed to search for the root cause problem and then take help to fix it.

This type of error can be because of not proper installation of outlook or there must be sent/receive an error in your outlook particularly error 0x8004210a. Although I read this that the real cause behind error 0x8004210a in MS-Outlook is the incorrect handling of account settings primarily SSL layer authentication, port number, and other relevant settings. So it's hard to get it fixed, but still, there are some defined steps which I have followed and suggesting you to try. 

Hope it gets fixed!! 

[#5]

Couldn't find the exact image while trying to resolve the above issue.@Deepak335 This is what i am seeing below. Thanks 

[#6]

Just check the outbox of outlook. If your mail is there delete it. While deleting just turn off your wifi or internet because if you are connected it will not allow you to delete the mail