How to block incoming e-mail?

declare it as spam and it can block that way

Spamming them won't block them----you'll still get the mail, just in the spam folder instead of the inbox. AND----that's find if you're talking about Spam Mail. But if you're talking about more personal mail---block their address. You can block their address and Yahoo will delete any future emails arriving from that address immediately----and you'll never see any of them. That email will NOT be returned to the sender (Yahoo deletes it), and they aren't notified that they have been blocked (for security reasons). They will think you're still getting their emails and are just ignoring them. Mail page>>options>>mail options>>Spam (from the list on the left)>>block addresses. Enter that exact address in the space provided>>click "add block">>THEN click "save changes" at the top of the page.