After I signed up for IM, I now receive LOTS of SPAM. Why? How to get rid of it, other than delete?

When I sign up for a new service such as IM, I usually sign up under a throwaway address like mailinglists4me@gmail.com . Yes that is a real address.

That way I can stop using that account anytime I get deluged by spam.

Now on to your immediate problem, I would suggest downloading Mozilla Thunderbird to be your email client. It has sophisticated filters for blocking spam mail and it's free.

Another method would be getting a Gmail account, forward your present incoming mail to the Gmail account, and then create a rule sending all mail received in that gmail account back to your inbox.

The spam filters on Gmail are very sophisticated and I receive very little spam. When I do receive spam I flag it as spam and Gmail learns that that type of mail is spam.

I wish you luck. Spam is so annoying.