These are the main and most frequent causes of duplication of emails in Outlook.
It can intercept sending or receiving an email, thereby duplicating messages.
For example, if the user independently copies and inserts appointments in the calendar, he may accidentally duplicate them. This also leads to duplicate mail until this problem is fixed. Because of this, conflicting rules can operate simultaneously and, as a result, you get duplicate messages, calendar dates, records, etc. As a result, the program places messages in the Inbox, but cannot define them as Synced. Here we are talking about a low update rate for received messages. The sending or receiving intervals are too short. As a result, you’ll get some duplicate data.
Perhaps you have several identical accounts and each of them receives the same message. Incorrect settings in your account or mailbox. 6 reasons for duplicate emails in Outlook
