How can I find out if my e-mail account was breached by anouther person / computer?

My X husband is stocking me,and my pastor at church caught my X husbands niece trying to access my yahoo e-mail account on the church computer...How can I tell if she accessed it or not?How can I find out if my e-mail account was breached by anouther person / computer?There is no easy way to find out who is accessing your e-mail. The only sensible answer is to immediately change your password. Try setting your e-mail account to save deleted mail so that you can see if someone is removing items. Or look to see if there is opened mail that you have not personally read.