Hi @Dort, ME van (fgb) ,
Welcome to our forum!
Did you try to select and drag the message you want to attach from the message list to calendar events in New Outlook for Windows?
If so, based on my research, i found that we can only select and drag the message you want to attach from the message list to new/replied/forwarded email, but not to calendar events in New Outlook for Windows. As a workaround, it's suggested that you could save the email to local and then drag it or click the paper clip icon to attach it to the calendar event.
Please kindly understand that many functions are not designed at present. At present, what I can do for you is to submit feedback for your request and I have post here, and you could vote for it. If you have any suggestions or ideas, It's suggested that you could post here. Hope Microsoft will notice this in the future. Thank you for your understanding and support!
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