Why are emails I send with attachments not being delivered?

I have noticed that a number of my emails w/attachments have not been delivered. One ISP actually told me the email was not delivered. I divided it into 2 emails w/attachments of less than 100kb and it seemed to be delivered. Could this be my problem (I have and pay for Hotmail and receive large files up to 20mb regularly) or a problem with my correspondent's email account?

I received a comment today, October 31st, that the link to Leo's site was not working well. Therefore I changed the link to his home page. The article about the emails w/attachment is on that home page now. If it has moved when you go there simply do a search on his site for that article. Don