"Sent By" problem while deleting an attachement

While trying to delete an attachement from an email in my inbox, something weird happend in which every one in the mail list (to and CC) has received an email from the original email sender with a Sent By line indicating my name.

I am not delegated to send an email in behalf of that person, and I don’t have that authority.

This has happened before, last year, the same exact issue happened to me. It was different company and different user.

I would like to know if there is any key stroke combination would perform this job. It is scary.

Thanks

Sausan