How do I delete my two sisters from emailing me, is there anyway to block them?

Go to the Spam / Bulk folder and see if the email that you spammed is there. If so, mark it as Not Spam, which will return it to the Inbox and remove the block against the address automatically. (If you are using the classic version of Y.Mail, you have to open the email to find the Not Spam button.)

If the email that you spammed is no longer in the Spam / Bulk folder, you can manually remove the address from the block list. Here's how...

If you use the New Yahoo Mail version (formerly known as Beta), go to Options -> Mail Options -> Spam. If you use the Classic version, go to Options -> Block Addresses.

Look for the address in the list of blocked addresses. The list is in num/alpha order. When you find it, select it and click Remove Block. You will then be able to receive emails from that contact as usual.

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If you really do not want to get mail from them, you can block their addresses.

Look for the 'Options' link at upper right corner of mail screen and click on it

Options /mail options

Click on 'spam' in the list on the left.

Then in 'Blocked Email Addresses,' enter the E-mail address you wish blocked, in the box after 'Add a blocked address' and click on the 'add' button, then click on 'save changes' at top left of screen.

You will never get mail from that address again.

depends with email server u use,but i am sure there is a way,have a look and u probably can mark it as spam or something,then it wont allow them to send anymore emails