I hadn't changed anything on my iPhone or Yahoo email settings, and last night I got a popup error on my iPhone telling me in a popup message that it was unable to send an email message because my password was incorrect. Even though I went into the email settings and changed it to what I know is correct, it still didn't let me send, at which point I just went to bed. Today so far, though, I'm able to send and receive like normal. What would cause my phone to do this?