I have to disagree Stefan,
There is an error at work here, but there is also the issue that any doc sent by email turns up on the other end as READ ONLY.....and that is Microsoft protecting me when I don't want to be.
Are you using Outlook for e-mail? Outlook (2010, if I remember correctly) removed the ability to edit e-mail attachments without saving them to the local drive first, and for a very good reason, I believe. The reason was that many people used to edit attachments
opened directly from an e-mail and then they lost their changes when they closed the attachment. Of course, you could argue that this would only happen to inexperienced users. Anyway, my point is that if you want this to change, you have to post a suggestion
in the Outlook section of the Uservoice forum at https://outlook.uservoice.com/forums/322590-outlook-2016-for-windows. Or you could use some other e-mail program, of course.
In the message to which you replied, I specifically commented on the permissions issue only: "Note that when you see a message referring to permission issues, it isn't Microsoft trying to protect you from yourself. On the contrary, you have run into an error,
of course."