--It depends. If it is one of those 'Englishmen Irishmen Scotsmen' jokes we've heard all our lives I would continue as you are - ignore and delete them. However, if it isn't really a joke, if it is one of those misinformation emails, such as those emails 'laughingly' telling about all the benefits immigrants/other ethnic groups get that mainstream people don't, I would send it back to my friend with the actual facts. I did that once, and the friend was grateful, not cross. She was cross with the friend who had sent it to her though.
I got the true information and statistics from my MP. I sent him a copy of the email and told him it was circulating, obviously mostly untrue, and I needed true facts and stats. He not only gave them to me, but he gave me detailed info about the origin of the email (Canada), which had been adjusted to suit Australia, where I live. He said it was circulating in slightly altered forms in the UK, US and NZ, as well as Canada.