Assuming its Thunderbird ( dont know the latest layout, refuse to use it)
Have a read    Article here
One way to tell if its Thunderbird ( assuming you are using it) go to outlook.com, sign in to the mail see if they are duplicated there. if not then its the email program.
Another cause can be if you have the account twice, check accounts to make sure it's only there once.
Have a read    Article here
One way to tell if its Thunderbird ( assuming you are using it) go to outlook.com, sign in to the mail see if they are duplicated there. if not then its the email program.
Another cause can be if you have the account twice, check accounts to make sure it's only there once.
Upgrades = Old bugs replaced with new Bugs.