My iPhone 4 just started this crap today as well. The message I first received this morning was "The user name or password for "apple.imap.mail.yahoo.com" is incorrect." I logged in fine with the Yahoo app and web versions, so I deleted it and re-added it back. still no success.
At one point I was getting the port 993 timeout.
I went to the web version and changed my password, just in case some requirement changed to alpha-numeric and no success. Same messages.
I deleted Yahoo, powercycled the phone and re-added it again, no success.
I created a new account in Yahoo and set it up and it worked????????? Ta Da
I went back and changed to my original account that I've had for 9 years and same user name or password problem, "The user name or password for "apple.imap.mail.yahoo.com" is incorrect."
I know the user name and password are correct because I just logged into Yahoo mail on the web and the Yahoo app without issues.
Apple and Yahoo need to partner on this issue. I'm losing interest in my iPhone real quick. It's about time for an upgrade anyways.
I made a change that I picked up from another member on the board:
This is how I just fixed the problem, at least for now. There seems to be a problem with the smtp address when using emails ending in ymail.com
I fixed it by
1) go into settings on your iphone/ipad
2) go to Mail,Contacts, calenders... settings
3) choose the email account your having problems with
4) click on your Account ***** @ ymail.com etc
5) at the bottom it says " SMTP Yahoo! SMTP Server >" choose that
6) Click " Add server...
7) type " stmp.mail.yahoo.com " leave the user name and password blank.
everything should work. but it just takes a little extra time to connect because it first tries the original smtp server but fails, then tries the one you added and works.
I retested my iPhone Mail, I cannot see anything in my Inbox. I tried to send a test email anyways and I was successfully able to send a test email to my own email account and a second account.
I still cannot get incoming mail on my iPhone or see my IN/SENT history, but know it's connecting enough to send emails. Error "Cannot Get Mail" still occurs.