If, in Yahoo! Mail it is but the ad to the side of your message that keeps you from seeing its full width, help is but a click (or two) away: you can hide the ad for the current message.
Yahoo! Mail Plus, of course, shows no ads at all.
Hide Ads and Make More Room for a Message You View in Yahoo! Mail
To temporarily hide the ad on Yahoo! Mail's side and have more room for viewing the current message (or mailbox):
Note: the following is currently not available with Yahoo! Mail.
- Click the Hide Advertisement arrow that separates the ad from the email or message list.
- If a message appears, click OK.
(Updated July 2011)