How do I stop deleted emails from subsequently downloading again and again?

Look into the settings for that e-mail account. Settings, e-mail, contacts, calendar, and then the account itself. You want to see if it has the option to 'delete from server'. Delete it from the server and it won't keep downloading.

Go to

Settings > Mail, Contacts, Calendar > Your Account Name > Advanced > Delete from Server > when Removed from Inbox

is there a way to do this so i can delete it from my computer but not my server? and not have it come back into my computer?