This method changes the name, the subject (title) and the preheader of several existing emails at once,
each with its own values. Only the passed fields change; the content of the email stays as it is.

• A field that is not passed (or is null) is kept.
• An empty title or preheader clears it. name cannot be empty and is up to 200 characters.
• The preheader is plain text: markup in it is stored as text.
• Up to 500 items in one request; an id may appear once.

The update runs in the background: the response carries an operationId, and the outcome — which emails
were updated and why the others were not — is read with Get the status of an operation within 15 minutes.

An email is not updated, and is listed in the outcome with a reason, when it is not found in the project
(NOT_FOUND, also for an email of another project), is a draft (DRAFT), is a translated version
(TRANSLATION_VERSION), is opened in the editor right now (OPENED_IN_EDITOR — repeat the request later),
is passed more than once (DUPLICATE_ID), or could not be saved (UPDATE_FAILED).