When I type the message it looks like this:

When I go to the outbox it looks like this:

When I open that message from my outbox it looks like this:

Here is the calendar item:

You notice this item is not even in my current calendar but in an archive of old calendar items I keep on my harddrive. I should mention I have had this practice for many years and never experienced this problem before. As far as I know, when this problem arises it always links to an old calendar item, never something recent. Also, in case it is relevant, the person I am sending the email to had nothing to do with the calendar item, in fact I was not even in possession of that persons email address at that time.

As a reminder, the above problem happens with a number of email addresses but not all and each email address is linked to a different calendar item but always the same one for that address.

Hi,

Does this issue happen when we open Outlook in safe mode? Press Windows key + R to open the Run command, type outlook /safe and press Enter. If the problem would be gone in safe mode, please go to File > Options > Add-ins and disable suspicious add-ins to fix the issue.

If above does't work, I'd recommend we create a new mail profile in Control Panel and then reconfigure your email account in the new profile to see the result. To do this, please refer:

https://support.microsoft.com/en-us/kb/829918

Regards,

Steve Fan
TechNet Community Support