Jun 27, 2019  As the IT guy, my Exchange mailbox is set up on four devices - laptop and desktop which are both Outlook 2016. Plus my iphone and mac mini - on the latest iOS and mac OS X. No idea if those details contribute to the issue. Did this as both my regular user and my more privileged administrative user. Issue persisted.

When using Mail for accessing your e-mail, you might run into a problem where Mail repeatedly asks for your password, either when you are checking for new messages (such as when opening Mail for the first time), or when attempting to send messages.

This can be frustrating to deal with if it happens, but if it does there are several things you can do to fix the situation.

Toggle your internet off and on

Use this menu to disable Wi-Fi, and then re-enable it.

Often Mail prompting for a password is from its inability to properly connect to your service provider. This can happen if you have lost your connection in the midst of communicating, so try toggling your Wi-Fi or other network connections off and then back on, to see if this helps the situation.

Wait a short while

It may be instinctive to try entering your password repeatedly in the authentication window that pops up, followed by clicking the “Get Mail” button to ensure it takes; however, while worth one try, if the password box pops up again, then this approach is likely a waste of time. Sometimes odd problems with mail account servers can prevent authentication for a short while, so if this happens, consider waiting about 10-15 minutes before trying again.

Quit and relaunch Mail

In addition to waiting, quit and relaunch Mail to see if the problem is simply a temporary fault with how Mail’s configuration has loaded.

Ensure the password is correct

While passwords should be stored in your Mac’s keychain, if you have entered the password again and then re-saved it in your keychain, then you might have simply entered it incorrectly. Therefore, try again and ensure you have put in the right password.

Open the Keychain Access utility, and search for the affected e-mail account (username and domain) to locate any keychain entries used for accessing this service. Select any relevant ones (especially if there are duplicates), and delete them from your keychain. Following this, go back to Mail and supply your password when prompted, and choose the option to save the password.

In addition to using the Mail password prompts, you can manually enter passwords in Mail’s settings. This may be especially pertinent if the password prompt is only happening when you try to send mail, or when you try to receive mail:

1. Enter your passwords in Mail’s preferences for the SMTP server as well as for your incoming servers.

   Go to Mail’s preferences and click “Accounts” (not the Accounts option in the Mail menu)

2. Select the affected account in the list to the left
3. In the Account Information tab, update your password in the “Password” field
4. In the Outgoing Mail Server (SMTL) menu, choose “Edit SMTP Server List…”
5. Select the SMTP server you use with this account
6. Click the Advanced tab
7. Again re-type your password, followed by clicking OK to save

In addition to updating your password, ensure your outgoing server’s port number and SSL options are set appropriately, according to the configuration requirements for your mail service. You might need to search on the Web or otherwise with your service provider to see what these settings are. Lastly, try toggling the box to automatically detect and maintain account settings, to see if this setting may be causing the problem.

If you see any errors when verifying your keychain, then run the repair routine to fix them.

Repair keychains

Mac Mail Keeps Asking For Exchange Password

If re-entering passwords does not seem to fix the issue, then try repairing your login keychain. To do this, open Keychain Access and select your keychain, followed by choosing Keychain First Aid in the Keychain Access menu (or press Option-Command-A). In the window that pops up, click Start to verify, and if you see any problems pop up (especially if they are related to your mail account passwords), then click the Repair radio button and again click Start. Following this, you might need to re-supply your password again to save it.

After you or your Mac administrator resets the password of your macOS user account, your Mac might ask you to update your keychain password or enter the password of your login keychain. It might also tell you that the system was unable to unlock your login keychain. That's because your login keychain is still using your old password.

If you don't know your old password

If you don't know your old password, the solution is to create a new login keychain.

If you know your old password

If you know your old password, use that password to update your existing login keychain:

Mac Mail Exchange Keeps Asking For Password

1. Open the Keychain Access app, which is in the the Utilities folder of your Applications folder.
2. From the list of keychains on the left side of the window, select 'login.'
3. From the Edit menu in the menu bar, choose “Change Password for Keychain 'login.'”
4. Enter the old password of your user account in the Current Password field. This is the password you were using before the password was reset.
5. Enter the new password of your user account in the New Password field. This is the password you're now using to log in to your Mac. Enter the same password in the Verify field.
   
6. Click OK when done, then quit Keychain Access.