How do I sync mail in my iCloud account on my iPad / iPhone with what is on icloud.com or my iMac?

How do I sync mail in my iCloud account on my iPad / iPhone with what is on icloud.com or my iMac? I windup with over 5,000 messages takes all day to get rid of! Mail seems to be the worst mail program out there. Some one needs to re-engineer this program. Would be nice if you could do select all and send to trash out of the in box like you can on the iMac.