Use yahoo app for iphone or add another email account as type Other and google the settings for yahoo pop access.  Worked for me, not ideal but you at least see your email.

• Incoming mail server settings:
  • POP server: pop.mail.yahoo.com
  • Use SSL
  • Port: 995
• Outgoing mail server (SMTP) settings:
  • SMTP server: smtp.mail.yahoo.com
  • Use SSL
  • Port: 465
  • Use authentication
• Email address: Your Yahoo! Mail email address (for example,jo.bloggs@yahoo.com)
• Password: Your Yahoo! Mail password
• Account name/sign-in name: Your Yahoo! ID (your email address without the "@yahoo.com" at the end; for example, "jo.bloggs")

Don't forget to go into smtp setting and add the username and password there if you want to send mail  After yahoo gets the imap issue fixed, just disable this account in iphone settings to use as a backup in case yahoo imap goes down again.

Just got a response from Yahoo acknowledging a problem, and offering the temporary workaround (use a web browser to access yahoo mail instead of the native mail app on the iphone.  Good to know that they know there's a problem and that they are working on it.  Hope it's fixed soon...

ecently you requested personal assistance from our on-line support center. Below is a summary of your request and our response.

Yahoo! Mail users see "Invalid ID and password" errors when using mobile device

ID: SLN7959

Refers to: Mail , Mail Classic , Mobile Mail

Description

This article addresses an issue where users are unable to access their Yahoo! Mail account on a mobile device due to an "Invalid ID and password" error

• I can't access my Mail account.
• I see an "invalid password" error on my mobile device

Resolution

We have received reports that some customers are unable to access their Yahoo! Mail account on a mobile device because of an "Invalid ID and password" error.

Status: Our Engineering team is already working on the resolution now and we intend to have it corrected as soon as possible.

Workaround: Login using mobile web browser: http://m.yahoo.com/

Don't forget to go into smtp setting and add the username and password there if you want to send mail  After yahoo gets the imap issue fixed, just disable this account in iphone settings to use as a backup in case yahoo imap goes down again

Thanks:) I tried the POP avenue but I did forget to do this and wondered why I could receive but not send

SO, this issue is still going on this morning??? Any update from yahoo?

No response back from Yahoo to me yet other than the first response (posted above) from yahoo acknowledging the problem and saying they are working on it. 

I still cannot access mail from yahoo imap via iphone or ipad native mail app. 

I can access via web which is ok-ish temporarily (next day or so). 

Signed up for a hotmail account last night and have this waiting in case yahoo doesn't fix this.  Have a gmail account that I don't use and was considering to start using that till I came across multiple horror stories about people mysteriously losing their gmail emails and there contacts.

It's back up and running on my iPhone, still no connectivity through Outlook.

Having this issue as well.  No problem connecting through Yahoo's website or through the Yahoo app, but it will not connect in order to push email to the iPhone.

Same Problem here 2nd day with the same issue, I have two Yahoo email on the phone, the first one working fine the 2nd stopped working two days ago with same message "apple.imap.mail.yahoo.com' error. able to check email on my desktop, yahoo mobile app but not using iphone mail..

I started having this problem yesterday morning and still cannot get my messages. Very frustrating especially since I've been having problems with Yahoo pushing emails for months. It's also killing my battery trying to check for mail.

So go complain to Yahoo. The problem has nothing to do with Apple at all.

Just got this response from Yahoo help..

Ricky: We have received reports that some customers are unable to access their Yahoo! Mail account on a mobile device because of an "Invalid ID and password" error.

Ricky: Our Engineering team is already working on the resolution now and we intend to have it corrected as soon as possible.

CD-SR, Thanks for the pop & smtp info. Tried it and no luck. same status. Cannot Get Mail error.

Works fine accessing in any other method, web, Yahoo mail app, but not iphone mail.

Glad AdiHo got the same sort of answer as I did (they know of the exact same issue we are having), and was glad to get an official yahoo link acknowledging the problem.  At least now we know someone is trying to do something about it.  Hope it's fixed soon...

http://help.yahoo.com/kb/index?page=content&id=SLN7959&actp=support&locale=en_US &y=PROD_MAIL_ML&i=+6Q0pgwl9BwsA51AEAt2zg==

CDSR'S POST WORKED!! THIS IS WHAT IT SHOULD LOOK LIKE.

GO TO MAIL, CONTACTS

SELECT ADD ACCOUNT

FILL IN UR INFO

PUT THIS PIC FOR YOUR INCOMING INFORMATION

THIS FOR YOUR OUTGOING

AND THIS IS MY SETTING UNDER THE ADVANCED TAB

HOPE THIS HELPS.. AT LEAST UNTIL YAHOO SERVERS ARE BACK UP

you have to pay for yahoo to be on your mac or ipod if it is yahoo.com but if it is yahoo.ca, you should be fine