Authentication Failure for Mail on iPhone

okay i figured it out! go into mail app and into the account that’s not working. tap the mail slider to off position. wait a second or two and then flip it back on; it will prompt you to log in and whalah! mine had been off for almost two weeks and i couldn’t figure it out. turns out its an intuitive fix—hope you’ve all can find resolve!

"Authentication Failure for Mail on iPhone: When I go into mail, I am getting an error message. Authenticationfailure. Authenticate invalid credentials. I’m not aware of changing anything. It Worked yesterday. I’ve tried to find an answer on the internet with no success. Can someone please help me fix my email? Thank you."

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Fixing your Credentials:

A. Use a New App Password:

Note that you may need a new App Password, being that Mail is a third party app. You cannot log in using your eMail address password. As an example, you'd go here for gmail: Sign in Using App Passwords - Gmail Help - Google Support

No success?...

B. Add the Account Back:

I've seen quite a few relevant report on this since iOS18 and Sequoia, in regards to Outlook/Hotmail accounts in the Mail app. The solution for that is to remove the eMail account, and then add it back, using the exchange option.

okay i figured it out! go into mail app and into the account that’s not working. tap the mail slider to off position. wait a second or two and then flip it back on; it will prompt you to log in and whalah! mine had been off for almost two weeks and i couldn’t figure it out. turns out its an intuitive fix—hope you’ve all can find resolve!

Here is the fix!

Go to i phone settings> Scroll down & click on apps> Scroll down & click on Mail app> Click on Mail accounts> Click the Mail account your error is referring to> switch the mail slider to off then back on. It will then prompt you to sign in, once signed in it should be fixed. If error is till occurring, once again make sure the mail slider is turned on.

Had this error for GMail. I fixed it by toggling the Mail off in the Mail settings for GMail, then back on and re-logged in. Then, I logged into the GMail account via the browser. I went to manage account, then Security. There was an error about an attempted login and it wanted me to confirm that it was me. I confirmed, and my email worked.

Generate an App Password

1. Open a web browser on your computer or phone and sign in to your Yahoo account.
2. Go to your Yahoo Account Security page. (You may need to search "Yahoo Account Security" if you can't find the direct link).
3. Click on Generate app password or Generate and manage app passwords.
4. From the dropdown menu, select "Other App" or a relevant option (like "iOS Mail").
5. Enter a name for the app (e.g., "iPhone Mail") and click Generate Password.
6. A unique, 16-digit password will be displayed. Copy this password immediately—you will not see it again.

If your mail providor is Yahoo, Go to this link yahoo mail failed to authenticate - Apple Community and do what it says there. Note the instructions are for a Mac, but the basic idea is 1) delete the existing mail account on your iphone, go to Yahoo and get an “app password” and then create a new account with that password as if you are not a Yahoo user.

Turning the phone off worked for me as I’d done all the other things suggested but until I turned the phone off and on, it wasn’t working. Thank you. Something so simple and effective.

You can also try by deleting the email account in the app.

Go to Apps>Mail>Mail Accounts>Tap on the Mail Account. Once deleted restart you iPhone and re-enter your account.

Try re-starting your phone. This along with what you did resolved my problem.

I had the exact experience and rebooted and the problem was fixed.

Not true. I have 2 yahoo emails and only one had "failed authentication" msg after I updated my IOS. The other was perfectly fine.

The update affected other password areas too, unrelated to email, which I resolved.

Taking the advice of "queenbeefastliveslow" plus whomever suggested re-starting phone solved it for me.

Power iPhone off. Wait 10sec then power back on. Open MAIL app and emails should start to download.

I changed my Apple password, and got the authentication failure. It fixed itself after I synced the phone with a lightning cable.

Well, if nothing is working for you then I would delete the app and reinstall it.