However, you’ve probably never paid attention to a hostname.

They usually provide a transition that lasts months or years and send updates via email warning of an upcoming deadline, after which the hostnames will stop working.

Mail-hosting companies do sometimes change the hostnames of their incoming and outgoing mail servers. Create a new app-specific password and see if that solves the problem. These passwords should remain working forever, but sites may reset or expire them for security reasons or their own policies. These passwords, which you create on those companies’ account-management websites (like ), only allow syncing with those three kinds of services.

App-specific password expires: Many multi-service hosts, like Apple and Google, opted years ago to limit the risk of exposure of an account via calendar events, contact cards, and email message synchronization by creating app-specific passwords.

To resolve this, you will have to create a new password via the host’s website. (If you provided an alternate address for contact, they could send a message there.) Because you can’t know, it’s a good reason to check your mail host’s website or status page, as explained above.

There’s no way for the company to reach you other than via email.

Host resets password: When there’s an attack against a service that manages accounts (mail or otherwise), they may take the prudent step to reset all passwords whether or not they know a successful breach occurred.

(I use Postbox and it provides a special pop-up web sheet in a window for this purpose.) For one of my mail accounts, I have to refresh my email token weekly with a fresh login or access email is blocked. This occurs largely with corporate-style mail systems and web-hosted ones deployed by Google, Microsoft, and others for small and large businesses alike.

Token expires: You’re using a connection that creates a token stored in Mail, and the mail server causes that token record to expire.

However, there are some circumstances in which your legitimate email account and password need re-entry or a new password created: Your settings should never become corrupted: there’s no reason to re-enter details that were perfect the first time around. An app-specific password may have expired or been revoked.

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