Mavericks and email

I have Mavericks as an update on my iMac. Previously I had Snow Leopard and had no problems with email at all. Now I cannot open more than half of my emails because they were generated on PC's. Is there a solution to this? Am i unique with this problem?I cannot even open an eCard. What happened to "if it ain't broke then don't fix it"
Douglas

Yes, the situation you're describing is unique to you. Neither your Mac nor your ISP cares what computer system generated an email -- emails are standardized into common formats. Are you perhaps trying to say that some of the proprietary *attachments* in your emails can't be read?