There are many things that can be done to prevent this and likely often are.  I&#x27;ve set my mail client to color the subject line of messages differently if the from address is in my addressbook or not.  However, I don&#x27;t know how common it is for mail clients to do things like that by default so there may be many people who don&#x27;t have any obvious sign that something is wrong.<p>ETA: I think some slight variations on the domain name could also be filtered out completely, but I&#x27;d guess it would be hard to catch all of those that it is difficult to visually detect without also filtering legitimate mail.