If you're having trouble getting Address AutoComplete to work, try these troubleshooting tips:
1. First make sure Address AutoComplete is enabled.
Your mail account enables Address AutoComplete by default. If you've turned off Address AutoComplete, you'll need to re-enable it by ensuring the "Use Address AutoComplete (default)" option is selected. Learn how.
2. Make sure you're using a supported browser.
If you look above the "To:" field while composing an email and see no reference to Address AutoComplete, you are most likely using a browser that does not support this feature. You can still insert contacts from your Address Book by clicking on the "Insert addresses" or "To:" links.
Yahoo Address AutoComplete works on Windows and Macintosh computers in the following browsers:
Windows: Internet Explorer 5+, Netscape 7.2+, Mozilla 1.4+
Mac: Mozilla 1.4+