You can, but this only works if you're getting multiple messages from the same source. Are you?

If so, yes. Set up a filter! Click Options in the upper-right corner of the page and select Mail Options, then click Filters from the list on the left. Put the address you don't want any more mail from into the "From:" field of the Add Filter set-up. Then, in the final field—"Move the message to:"—select Trash.

The best way to block random junk mail—spam—arriving in your Inbox from multiple addresses is to use Yahoo! Mail's powerful SpamGuard protection. Make sure it's activated by clicking Options in the upper-right corner of your Mail page and selecting Mail Options. Click Spam from the list on the left, and look for a check in the box beside "Control SpamGuard".