Breaking: #105809 - AfterMailerInitializationEvent removed 

See forge#105809

Description 

The event \TYPO3\CMS\Core\Mail\Event\AfterMailerInitializationEvent has been removed. This event became obsolete with the introduction of the Symfony-based mailer in TYPO3 v10. It was only able to influence the TYPO3 Core mailer by calling the @internal method injectMailSettings() after the settings had already been determined. The event has been removed since it no longer had a meaningful use case.

Impact 

Event listeners registered for this event will no longer be triggered.

Affected installations 

This event has had little purpose since the switch to the Symfony-based mailer and is probably not used in most instances. The extension scanner will find usages.

Migration 

Check if this event can be substituted by reconfiguring $GLOBALS['TYPO3_CONF_VARS']['MAIL'] , or by listening for the event BeforeMailerSentMessageEvent instead.