Dean Said:

How can I get rid of the red underlines under every single word in my text when I write emails?

We Answered:

This option does not hold well with Yahoo at all. This is a browser spell check. If you have misspelled or if the word in not in the dictionary of the browser then it underlines the words with a red line.
To disable this option please go to Tools menu > Options > Advanced > General tab. Under browsing you can find “Check my spelling as I type” uncheck this option to disable the spell check and you cannot find the red lines if you have misspelled the words or while writing a mail.