Unable to log in to Mail on MacOS Sonoma

Hi ChelleChelleChelle66

welcome to the Apple (user-to-user) Community!

Re: Unable to log in to Mail on MacOS Sonoma

Wondering what happens when you try ... Eg: If an error message: it may help resolve the situation.

Else:

You may want to first try restarting your Mac (Apple Menu> Restart) and then log back in and see if you can now log in to Mail. (ie: Deletes temporary files, re-establishes connections, may update recent setting changes etc., and often restores order when something is not working as expected.)

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If more help is needed:

If you also use iCloud Mail, you might want to check that iiCloud Mail is turned on.

Eg: Choose Apple menu > System Settings, click [your name] at the top of the sidebar, click iCloud, click iCloud Mail, then check you have "Sync this Mac" turned on.

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Is the Account Enabled: Eg: Check that you have not accidentally turned the Account off:

Temporarily turn off email accounts

1. In the Mail app on your Mac, choose Mail > Settings, then click Accounts.
2. Select the account you want to stop using, then unselect the “Enable this account” tick box.

When you’re ready to start using the account again, just select the “Enable this account” tick box.

(Above is from Apple Support's article: Remove or temporarily turn off email accounts in Mail on Mac - Apple Support

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Seems you are using the Mail app to access your eMail account(s).

If needed: You could try going directly to the eMail provider's website (Eg: Yahoo, GMail etc.) to log-in and check all is in order there. There may a message there from the eMail provider, or, if your password is not working there, you can generally click a "forgot password" link to change it, and get a verification eMail.

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Re: My MacBook suddenly went offline for mail

When you re-gain access: For MacOS Sonoma:

See how to: Take email accounts offline or online in Mail on Mac - Apple Support

Eg: says:

"Take email accounts online

In the Mail app on your Mac, do one of the following:

• Take all accounts online: Choose Mailbox > Take All Accounts Online.
• Take a specific account online (if you have more than one account): Choose Mailbox > Online Status > Take [account] Online.

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If needed: For more information on how to use Mail on your Mac, see the Mail User Guide for Mac.

For more support / contact options etc. Mail Support Website: Mail - Official Apple Support

All the best :-)