Yahoo mail not sending emails

The solution for me was the capital letters. Just like sarahstauffacher, i had some capitals when i entered in my e-mail address with yahoo. I went back in and changed it and now my e-mails are magically sending.

I am having the exact same issue, except it's with my ATT Yahoo! account, which basically acts as a Yahoo! Plus email account. At first my email worked perfectly: email was being pushed to my iPhone and I had no trouble sending. But starting around August 1, I have noticed that none of my email is being sent. I get the little progress bar at the bottom of the screen that says "sending" (I turned the airplane sound off), but the "sent" email does not appear in my Sent folder and the recipient never receives it.

Because it has worked before, I'm inclined to believe that whoever is running that IMAP server (imap.apple.mail.yahoo.com) is at fault. After talking to Apple tech support, I was told that it was most likely a problem with Yahoo!'s servers. So then I called Yahoo! tech support only to be told that all their mail servers were working fine (the lady actually pinged all of them) and that it is most likely a problem with the iPhone.

It would be great if someone or Apple found a solution for this, but for now I just have it set up using POP, which works fine.

Just wanted to reaffirm you are not the only one having the sending issues. No emails show up in my SENT folder. My issue also started on Aug 1st, so it's no coincidence. Up until then, my SBC Global (ATT Yahoo!) mail account was working beautifully on the iPhone. This has been driving me nuts for the last 2 days and thought it was just me. Anyhow, I deleted the account and I've set it up using the POP settings (as opposed to the Y! Mail settings). Everything, including sending emails works fine. The drawback is no "Push" and no mapping of your emails. If you are willing to put up with this method for a few days until they get this obvious issue resolved, then the settings are:

Incoming Mail Server (POP3): pop.att.yahoo.com
Outgoing Mail Server (SMTP): smtp.att.yahoo.com

Be sure to enter your username and password for each.

Under ADVANCED:
SETTINGS:
Incoming Uses SSL: OFF
Outgoing Uses SSL: OFF

I noticed that if any of the SSL settings are set to ON, it will just timeout.

Good luck!

I'm having the exact same problem, although it seems intermittent. Some of my email is being sent correctly, and some is not.

If I use the POP settings, I am flooded with Spam which I did not have using the IMAP settings. It seems as though the IMAP settings filter the mail through Yahoo's spam filter but the POP settings do not. Is this normal?

Fixed my issue too...thanks for the headsup...